If you're a geology professor at a two-year college (community college, junior college, etc.), then please consider attending a planning workshop June 24 to 27 here at my campus of NOVA. My department and I are hosting, and the talented crew at SERC, including Heather MacDonald, are organizing. More details at the SERC website.

Labels: geology, nova, teaching

Happy new years! The grammar police return! A while back (May!), I commented on a few words that had gotten my attention through their misuse. Since then, a few more peaked piqued my interest, and now I return with the third installment of "Words' worth."

Peak / Peek / Pique - "Peak" means summit or maximum value; "Peek" means look at quickly or furtively; "Pique" means provoke or stimulate. You can "take a peek," but you cannot "take a peak" (unless you're involved in Appalachian coal mining). You can have something "pique your interest," but you cannot "peak your interest" in anything.

(Similiarly): Eke / Eek - People can "eke out a living" but they should reserve "eek" for unexpected encounters with mice.

Cite vs. site - a "site" is a place, either in the real world or on the web. You use "cite" when you're attributing work to someone else (or issuing a ticket, if you're a traffic cop).

Extinction vs. extirpation: extinction of a species or variety means there are none left, anywhere. However, the local version of the phenomenon is properly known as extirpation. Thus, if say you killed every single wallaby in Australia, but the wallabies on New Guinea were still numerous, you would have extirpated them from Australia, but you would not have made them extinct. Even professionals use "extinction" where they ought to be saying "extirpation."

Similarly, a lot of people use the word decimate "incorrectly." To decimate a population (say, of Roman soldiers) was to kill one out of every ten. 10% die, in other words, and 90% are left alive. That may be the official definition, but the truth of the matter is that the vast majority of people use the term decimate in exactly the opposite sense: that 90% die, and only 10% survive (or thereabouts). At what point do we switch the definition of a word: when 90% understand the meaning to be one thing, and only 10% stick with the old definition?

Shear vs. Sheer - There are many definitions to both "shear" and "sheer," but the one I see fuddled up most frequently is when people use "shear" to describe cliffs, or use "sheer" to describe geological stresses.

Oh dear: did you hear about the omission of "emission" on a Kansas state test (wherein some test-writer swapped the word omission for emission). Don't worry: the kids caught the error!

Literally - "Literally" means "actual," not an exaggeration, analogy, simile, or hyperbole, but actual truth. Amazing how many people use this incorrectly. Sometimes it seems like literally the entire world!

Metamorphosize - The first time I put up a post like this (see link above), I harped on the word "orientate." I pointed out that the word "orient" (verb) means the same thing, without an extra, unneccesary syllable. In spite of my harangue, orientate remains in the dictionary. Even worse, I find a lot of people want to throw an extra syllable in at the end of "metamorphose" even though "metamorphosize" is not an actual word.

Standing on line versus standing in line. This one seems to be cultural. Some people claim that when you queue up for, say, a movie, you're standing "on line." This grates on my ears, and I would instead say that you're standing "in line." (I reserve "online" for internet presence.) But I don't know that I am justified in feeling this way -- I think it's more likely that I just grew up in an "in" household, versus an "on" household.

As before, I'd like to know which words bug you. Chime in.

Labels: geologists, science and society, teaching, words

Last new year's, I stated some of my goals for the year. Here they are again; I'll bold the ones I actually accomplished, and strike through the ones that I didn't.

1. visiting the Galapagos Islands
2. visiting the high Andes (Cotopaxi, Chimborazo), Ecuador
3. finding a cool outcrop of graded beds in the Martinsburg Formation (late Ordovician turbidites in the Shenandoah Valley of Virginia) that Rick Diecchio told me about last week
4. "walking on the Moho" in Gros Morne National Park, Newfoundland (late summer)
5. seeing Snowball rocks and Ediacarans on the Avalon Peninsula, Newfoundland (late summer)
6. visiting Egg Mountain paleontological site, Montana
7. joining my colleague Ken Rasmussen's field trip to the Culpeper Basin, a Triassic rift valley in northern Virginia
8. some cool trip next winter break (2009-10): perhaps Patagonia? Or Antarctica?

I've also got some big teaching resolutions:

1. Running a successful and robust Structural Geology course for George Mason University (spring semester).
2. Running a successful and innovation Environmental Geology course for NOVA (spring semester).
3. Running a successful and safe Regional Field Geology of the Northern Rocky Mountains course for NOVA (summer semester).
4. Preparing and running a successful and groundbreaking Honors Historical Geology course linked with English Literature 242 at NOVA, where the English professor and I will bridge the two subjects with readings of Lyell, Darwin, "A Pair of Blue Eyes," and others (fall semester). (didn't get sufficient enrollment for this one; bummer!)

On other topics:

1. Finish my M.S.S.E. degree (July)
2. Buy a house
3. Put together a series of geology 'vodcasts' on local geology (though I've gathered a lot of footage that will eventually go into this series)
4. Write a few freelance articles [link]
5. Publish one cartoon per month in EARTH
6. Prepping (cutting and polishing) a backlog of rock samples from all over the place (I'll have to share the story soon of how our "Campus Safety Officer" emasculated my rock saw out of a fear of accidents and ensuing litigation: it's an absolute abomination...)
7. Successfully moving the geology department into our new building

So what's up for the coming year, 2010?

1. More structure at GMU! Bigger, better, tweaked towards greater learning.
2. Hire and train a new member of the NOVA geology team to take on some of the tasks that my colleagues and I can't currently keep up with.
3. Actually get up to Newfoundland this year. I've got a family reunion up there in early August, so hopefully that will be the catalyst. (My mom's side of the family are Newfies.)
4. Run my Rockies course (with co-instructor Pete Berquist) again.
5. Update my website's numerous mentions of "greywacke" (English spelling) to "graywacke" (American spelling).
6. Get my geoblogging under control. I'm clearly devoting too much time to this for too little recompense. Maybe an alternate would be: find a grant or some such to fund the time I spend writing this blog.
7. Continue my cartooning for EARTH. Also occasional freelance writing pieces.
8. Scan my Cartoon Guide to Geology and post it for download/printing on Lulu.
9. Take meaningful action as a "citizen scientist" to combat climate change misinformation, creationism and Intelligent Design mumbo-jumbo, and other forms of pseudoscience pertinent to my expertise as a geologist.
10. Get those geology vodcasts going.
11. Go to Antarctica. (fingers crossed)
12. Work less. Relax more. Be creative. Enjoy life.

Labels: antarctica, canada, climate change, evolution, montana, newfoundland, pseudoscience, structure, teaching

A couple of shots of the Thursday Physical Geology lab section, out hiking on the Billy Goat Trail:



A great group of students.... Photos courtesy of Judi Scharfman.

Labels: field trips, maryland, nova, piedmont, teaching

Got this yesterday via the NAGT newsletter:

REU Project in Yellowstone National Park

Greetings from Montana! We would appreciate your help in advertising to your students an NSF/GEO site project we will be running this summer on Evolution of the Precambrian Rocks of Yellowstone National Park (Dave Mogk, Paul Mueller, Darrell Henry, and Dave Foster PIs). Please visit the project website for further details. This project will be a comprehensive research experience that will include:

• Field mapping and sampling in Yellowstone National Park to contribute to a new geologic map of the basement rocks of YNP; students will work in small groups in the context of the larger project to define and address specific research topics in their area of interest; Dates: June 27-July 25, 2010;
• Direct experience in modern analytical studies including sample preparation, training on modern instrumentation petrologic, geochemical and geochronological; visits to analytical labs will be scheduled for fall semester 2010, and
• Presentation of research results, by submitting an abstract for a poster presentation at the Rocky Mountain Section meeting of the Geological Society of America, and participating in a group reunion meeting to contribute to a peer-reviewed journal article. Dates: Spring 2011, to be determined; Logan, Utah.

We are looking for a group of students (12) with diverse interests in geology to contribute to the research group. To unravel the geologic history of these Archean rocks, our research team will need students with interests in igneous and metamorphic petrology, sedimentology, geochemistry, geochronology and structural geology and tectonics. Students who have taken most of their geology “core” courses and have had a field camp (or other field experience) will be preferred. This experience will provide a great foundation for follow-on senior thesis/research projects at their home institutions. Please note that this will be a true back country experience in Yellowstone National Park, so students need to know that the daily routine will be physically challenging in this rugged terrain.

How to Apply:
Please send: a) Your letter of interest, stating what you hope to learn, what you can offer to this project, b) two letters of support from faculty or work supervisors, and c) your academic transcript . These materials can be submitted to (e-mail or mail):
David Mogk mogk@montana.edu
Dept of Earth Sciences (406) 994 6916
Montana State University
Bozeman, MT 59717

The deadline for applications is: January 30, 2010

Thanks in advance, and please, encourage your best, field-oriented students to apply!

Labels: field trips, maps, national parks, teaching, wyoming, yellowstone

On my Historical Geology field trip to the Massanutten Synclinorium, we observed oolites (ooids) in Cambrian-aged limestones deposited in the Sauk Sea. Like these:

Now the students have submitted their papers on that field trip. Grading the papers, I realized that some of my students were confusing how ~spherical oolites form (through chemical deposition on moving grains) with the perhaps more intuitive process by which clastic grains get rounded with transport. I made up this diagram to illustrate the difference between the two processes:



On the left, you see marine deposition in warm water becoming more concentrated in its load of dissolved ions as evaporation removes water (but not ions). Accordingly, chemical precipitation of calcite begins. Little grains on the bottom get a layer of calcite deposited over them. These grains are within reach of the wave base, so they get rolled in one direction, then rolled back again. As they oscillate back and forth, they expose "both their back and their belly" to the precipitating calcite, so they get concentric layers deposited: oldest in the middle, youngest on top. Like a gobstopper! Or a hailstone. They literally grow more spherical over time.

On the other hand, the right side of the diagram shows a chunk of rock, broken off from its source area, and tumbling downstream. As it travels, the sharp corners are most susceptible to being snapped off or abraded away, meaning that as it loses volume, it takes on a more and more rounded shape. This is physical weathering at work, not chemical precipitation. Note that even if it's very well rounded, that doesn't mean that it's necessarily spherical.

Labels: art, cambrian, field trips, limestone, primary structures, sediment, teaching, weathering

Next semester, the Annandale campus of NOVA has need for two instructors: one for a section of Physical Geology and a second one for a section of Historical Geology.

Both sections meet (in different rooms) Monday and Wednesday evenings, from 6:30 to 9:20 pm.

Minimum degree requirements: an M.S., with at least 18 graduate credit hours in geology. Remuneration is probably millions of dollars, though I'm not sure about that, and I'm sure that's not why you would want to do it, anyhow. Contact my boss, Dr. Craig Jensen, if you're interested: cjensen@nvcc.edu

Labels: geology, jobs, nova, teaching

Yesterday was the day we talked about dinosaurs and pterosaurs in Historical Geology. Accordingly, I dressed for the occasion:

(That is not me, by the way.) The t-shirt is by the very cool company Squidfire. I recommend you check out this design and their many other cool images on cool clothing at their website. Lily bought me this one - a gift much appreciated!

Labels: dinosaurs, fossils, gear, teaching

I've just submitted a list of the classes I intend to teach for summer 2010. Here they are on NOVA Geoblog, before you can access them in the official Schedule of Classes...

GOL 135 (070N) The Bedrock Geology of Washington, DC. HYBRID COURSE: pre-trip reading, field study and post-trip report. One-day field trip Saturday, June 12. Rain date: Sunday, June 13. Important pre-trip logistical information and preparatory readings located online. This trip will focus on the land upon which the capital city is built, including exposures in Rock Creek Park, Georgetown, and Adams-Morgan. Includes discussion of oceanic sediments, the Rock Creek shear zone, igneous rocks emplaced during Appalachian mountain-building, Cretaceous river gravels, dinosaur bones and recent faulting. Students will be evaluated with a field trip report which will be completed after the trip itself. NOTE: This trip involves moderately strenuous hiking on forest trails. Meet in back of the CT building at 9:00 a.m.; Return by 7:00 p.m. For information about meeting time/place or other questions call (703) 323-3276 or email cbentley@nvcc.edu
HYBRID course
Additional info online

GOL 295 (4 credits) Regional Field Geology of the Northern Rocky Mountains: July 10 to July 25, 2009. Pre-trip meetings Wed. June 9 and Wed. June 23, 6:30pm, in CS 217. Western Montana and Wyoming showcase tectonic, sedimentary, geomorphic, and volcanic features which provide world-class examples of geologic processes. Students in this course will complete field studies of locations in Yellowstone and Glacier National Parks, as well as several other field sites. The course will involve VERY STRENUOUS outdoor physical activity: Students are expected to hike several miles at high elevations in rough mountainous terrain in order to accomplish course objectives. Airfare, lodging, and transportation are covered in the approx. $1400 course fee (does NOT include tuition). For up-to-date information and a complete itinerary, see the course website or contact the instructor at cbentley@nvcc.edu or (703) 323-3276.
Extra fee
Instructor permission required
Additional info online

GOL 299 (071N) (2 credits) Snowball Earth. June 14-19, 2009. HYBRID COURSE: pre-course reading, lab, field study and post-course report. An episode of glaciation 700 million years ago, dubbed Snowball Earth, may have provided for the evolution of multicellular life. The Snowball Earth glaciations stretch our conception of the limits of climate change: the ice apparently reached from the Earth's poles to its equator! Scientists infer that the runaway freezing event was only ended due to volcano-induced global warming. This course examines the geological, chemical, and biological evidence for Snowball Earth, and includes a field trip to local "Snowball" deposits. Course meets four times: three evening sessions (6pm-9pm) in CS 217 and all day on a Saturday (9am-5pm). The schedule is: Monday June 14 (lecture), Wednesday June 16 (lab), Friday June 18 (discussion), and Saturday June 19 (field trip). For further information call (703) 323-3276 or email cbentley@nvcc.edu or go to the course website.
HYBRID course
Additional info online

Anyone in the Northern Virginia area who's interested in any of these classes, drop me a line!

Labels: dc, field trips, geology, montana, nova, snowball earth, teaching

Today I took a group of students to Sideling Hill, a syncline in western Maryland. Here are a few photos from the trip. All photos by my iPhone, via Facebook (which is why the quality is lower than my usual standards):

The group all kitted out at the Sideling Hill Visitor's Center (which was closed due to budget cuts in Maryland):


Jared points out fast-weathering shale layers betwixt slower-weathering sandstone layers:


Diamictite outcrop on the far western side of Sideling Hill:


More diamictite... enigmatic sediments...

Labels: maryland, nova, primary structures, sediment, structure, teaching, valley and ridge, weathering

"Earth and Mind," by the folks at SERC.

Labels: blogs, geology, teaching

Kim makes an elegant pitch for a bunch of cool projects on DonorsChoose.org. Wow! There's so much cool stuff up there. If you have ten extra bucks, please go send it to a needy Earth science teacher so they can get their students excited about geology. Thanks!

Labels: action, teaching

WHAT: Earth Science in the Spotlight: Engaging the Public

WHEN: Tuesday, Oct. 6, 5:30-8:00 PM; program begins at 6:15 PM.

WHERE: The Front Page Restaurant, 4201 Wilson Blvd., Arlington, VA, Located near Ballston Metro on the ground floor of the NSF building. Parking is available under the NSF building or at Ballston Common Mall.

WHO: Ann E. Benbow, Ph.D., Director of Education, Outreach and Development, American Geological Institute

HOW: Special 1/2 price burgers start at 5:30 PM. Please come early to order table service and socialize. Short presentation begins at 6:15 PM, followed by Q&A. No science background required- only an interest! Cafe Scientifique is free and open to the public. Register online here.

ABOUT THE TOPIC: The news media routinely sound alarms about natural disasters, climate change, and the energy crisis. But who helps the public make sense of these issues? More and more, scientists are stepping up to help ordinary people, from school children to policy makers, understand the earth science behind the headlines. Earth science, after all, encompasses virtually all the sciences, from biology to chemistry to physics. Learn how AGI, an association of 45 member societies across the geosciences, is tapping the expertise of professional geologists, oceanographers, meteorologists, and other scientists to improve education and promote public awareness on such timely topics. Join us for a brief discussion, exciting video and hands-on activities showing how you can play a vital part.

COMING NEXT MONTH: November 3, Mario J. Molina, Ph.D., Nobel Laureate in Chemistry 1995 will speak on ozone depletion in the atmosphere.

Labels: meetings, science and society, teaching

I went to the College of William and Mary for my undergraduate geology degree. One of the cherished rights of passage in that department was the "Geology 310" trip -- Regional Field Geology, often of the Colorado Plateau, but in recent years, the faculty have been running field courses to other locations. The program was written up in this fall's issue of the William and Mary Alumni Magazine. Check it out!

Labels: geology, teaching

My colleagues in NOVA's biology department were featured in today's Washington Post, which includes some photos of my building (the Shuler Building) and one of our labs. The point of the article is that community colleges in the DC area are adding classes like crazy to keep up with demand. The weak economy is blamed for the uptick in enrollment. Our student population increased by about 10% this semester. NOVA's numbers tower over other area schools:

Hat tip to Doug Dupin for alerting me to this piece!

Labels: nova, teaching

My colleague Ken Rasmussen and I were among ten faculty featured in a video that NOVA-Annandale Provost Barbara Saperstone commissioned to brag to the NOVA Board about all the cool stuff going on at her campus. If you're interested in watching the video (~17 minutes), it can be downloaded here. If you're only interested in the geology portion, fast-forward to 14:57 or so. (They saved the best for last.) Enjoy!

Labels: field trips, movies, nova, teaching

Last night, I took a group of Honors students to the United States Geological Survey's National Center in Reston, Virginia, for a public lecture by Bruce Molnia about Alaska's disappearing glaciers. The talk was all well & good, but a nice little surprise came afterwards, when Jared noticed a display in the lobby of the Dallas Peck Memorial Auditorium:

That's the classic "ancient Chinese seismograph" featured in so many introductory geology textbooks as the lead-in to their chapters on earthquakes and seismology. Pretty cool to see it in the flesh brass.

The way it works is that each of the little dragon heads projecting off the urn had a little brass ball in its mouth. If it got shaken by an earthquake, that little brass ball would pop out and into the waiting mouth of the little brass frog down below. The frogs aligned with the wave propogation direction would be the ones to be "fed." This implication of the temblor's source direction would allow authorities to direct scouts and relief operations to the appropriate corner of the dynasty.

Neat!

Labels: alaska, earthquakes, gear, glaciation, nova, rept, teaching

We just got a new position approved for our campus Science Learning Center!

Job Title: Science Learning Center Coordinator

Job description: Assist in setting up and coordinating the Science Learning Center. Provide lab help and advising outside of regularly scheduled class and labs. Provide help to science faculty for individual supervised classess, laboratories & undergraduate research. Work with laboratory assistants in reviewing & updating experiments. Organize study sessions and open study hours. Gather needed equipment and supplies; properly store and inventory these materials. Work with the Math, Science, and Engineering faculty, staff, and steering committees.

Degree Requirement: Bachelor’s Degree in Science, or equivalent training and experience. Master’s preferred.

Salary Range: $35,693-$53,345

Apply at our Human Resources page.

Labels: jobs, nova, teaching

One thing I've noticed when teaching Historical Geology at NOVA and GMU over the past four years is that students get confused between basins. There are depositional basins and structural basins, and they're not the same thing, though they both sag downwards in the middle. The other day while driving out to the Blue Ridge for a hike, a lightbulb went off above my head. I knew what I needed was a graphic that explicitly laid out the processes responsible for each structure, and their development over time. I jotted down a reminder to myself on the lid of the Starbucks coffee cup in my car's cup-holder.

When I got home, I translated the scrawled reminder into action. In my spare time over the past couple of days, I've been composing the basin graphic with CorelDraw. Here's what I drew:



Depositional basins result when there's a low spot on the Earth's crust. Water flows into these crustal sags, carrying sediment with it. Gradually, they can fill in. Sedimentary inputs are shown with arrows. (They can also self-perpetuate, as the heavy sediment keeps the crust sagging downward at that location.) Layers stack up according to superposition: oldest on the bottom, youngest on the top.

In contrast, structural basins have a different story. There, we start with an accumulation of sedimentary layers, and then we deform them into a basin shape. This deformation is the result of tectonic stresses which warp the rock layers. Erosion can then attack the downwarped strata, planing the "nested cups" shape down to a roughly horizontal ground surface. Sedimentary outputs are shown with arrows. The resulting outcrop pattern is somewhat like a bull's-eye, with the youngest layers exposed in the middle and the oldest layers exposed on the outer part of the structure.

In a depositional basin, the downward central sag comes first, and the stack of sediment is a result of that sag. In a structural basin, the stack of strata comes first, and the central downwarp is produced second.

________________________________________
If any educators want a larger version of this graphic for use in teaching, let me know. I'll happily e-mail you one. Also, if anyone would suggest any modifications to the graphic to make it more accurate or more useful for communicating these ideas, I'd be happy to get that feedback.

Labels: art, sediment, structure, teaching, words

Over the summer the rest of the geology department and I moved into our new home, the Shuler Building (CS) on the Annandale campus of NOVA. As part of our refurbishment, I got a nice new display case which is prominently displayed in the hallway of the second floor of CS, just down from our lab. For its inaugural display, I put together a collection of photos and samples from this summer's Rockies course. I think it looks pretty good:



If you're on campus, stop by and check it out!

Labels: gear, geology, montana, nova, teaching

Rockies co-instructor Pete Berquist was quoted in a nice little article appearing recently in Thomas Nelson Community College's internal newsletter. Here it is.

Labels: field trips, montana, nova, teaching

Please forward this post to anyone who you think might be interested. Thanks!

The Annandale campus of NOVA has an opening for an instructor to teach a Monday / Wednesday evening section of Physical Geology this semester. The class runs from 6:30pm until 9:20pm on Monday nights (lecture) and from 6:30pm until 9:20pm on Wednesday nights (lab). It is a four-credit course.

Applicants should have at least a master's degree in geology or a related Earth Science field. The general starting salary range for this position is between $730 and $862 per credit hour. The specific salary for each position will be calculated based on the selected individual's academic preparation and experience. Apply by sending a resume and expression of interest to Craig Jensen, Assistant Dean for the Physical Sciences, at cjensen@nvcc.edu.

I can provide any and all lecture PowerPoints, tests, and ready-to-go lab exercises for the instructor, if they so wish. We can make this really easy! (The instructor also has complete academic freedom to teach the course as they see fit.) NOVA students are diverse and fun, and this is an excellent opportunity to try out some teaching if you've never done it before, or if you're just looking to earn a few extra bucks sharing your knowledge.

Please don't hesitate to contact me or Craig with any questions!

CB

Labels: jobs, nova, teaching

Following on this morning's video from Jason, here are a few more Rockies class final projects:

Ringing Rocks (Bob)
Lewis & Clark Caverns (Charlie)
Gros Ventre Landslide (Chris)

Labels: montana, nova, teaching, websites, wyoming

In October of last year, I presented a list of my favorite analogies for geological processes. Effjot followed up with a visualization of one that was presented in the comments.

Today, I'd like to add to that list with three more evocative analogies.

Hydrothermal disseminated deposits are sweat stains.
Certain types of ore bodies are thought to be "sweated out" from magma chambers as they intrude to shallow enough levels in the crust. The shallow depths have low pressures, and that encourages the magma to devolatilize. The resulting hydrothermal fluids pick up lots of consitituents like sulfur and metals and stream away from the pluton. As they cool off, the dissolved constituents become supersaturated and begin to precipitate out as mineral deposits. These hydrothermal disseminated deposits end up in the pore spaces of surrounding rocks, or filling in cracks. This is kind of like how your body sweats out a solution of dissolved salts in water. When the water evaporates, the salts precipitate out wherever they find the space:

Sills are a funny kind of peanut butter sandwich.
A dike is an igneous intrusion which cuts across local stratification of the host rocks. Sills, in contrast, exploit the weaknesses between strata and inject their magma parallel to bedding. I think of this as being like using peanut-butter-in-a-tube to make a peanut butter sandwich without separating two pieces of bread. Like this three part series:




Exotic terranes are roadkill.
I show the following sequence of images to my Physical Geology students when discussing how exotic terranes accumulate on the leading edge of a drifting continent:








... and I think you get the idea. That one kind of speaks for itself...

How about you? Got any good analogies for relaying geological concepts?

Labels: analogies, art, humor, ore, teaching

Labels: art, evolution, nova, teaching

Just found out about a cool website with animations describing lots of geologic processes and products. The site is hosted by the University of Tromso, Norway, and most animations are available in both English and Norwegian. Check it out!

Hat tip to Pete Berquist for this link!

Labels: art, geology, teaching, websites

So, it's a month until my Rockies class starts. I've been encouraging all the students to get in shape, because the high elevations, rough terrain and multimile distances we'll be hiking in Montana and Wyoming could really kick an east-coast flatlander's arse. So we've scheduled a few training hikes to help everyone physically prepare for the Rockies experience. Last weekend, we did a 5.5-mile circuit up the steep Little Devil's Stairs trail in Shenandoah National Park. I was joined by five Rockies students + one of their kids. Here's a map of the loop we did:



Here's a few photos of the hike, and the geology we encountered along the way:



John poses next to some jointed columns in the Catoctin Formation, a Neoproterozoic rift-related series of flood basalts (subsequently metamorphosed during Alleghenian mountain building).


End-on view of one of the columns:


Overhanging cliff showing columns weathering out along jointed surfaces:


Bob poses next to a cliff, helping me demonstrate how difficult it is to take a well-exposed photo in the jungle of the Virginia hardwood forest:


A wiggle in some columns:


Jared thought these columns were better than the first ones he saw, at Old Rag Mountain.


Here's me with a fifteen-foot-long section of columns, indicating that the flow from which this boulder was derived must have been at least fifteen feet thick, maybe more:




But it wasn't all columns. There was also a lot of column-less massive Catoctin Formation, and some nice inter-flow conglomerates which are interpreted as stream deposits that developed atop a cooled flow before the next flow erupted. These conglomerates imply a reasonable amount of time passed between successive eruptions of the Catoctin flood basalts. The lichens obscure the rock, but note for instance the fingernail-sized chunk of greenstone an inch above my hand:


More chunks in the conglomerate:


And more:


Jared guards the way forward:


The view from the top:

Labels: basalt, iapetus, igneous, metamorphism, nova, primary structures, proterozoic, sediment, shenandoah, structure, teaching

This semester, I employed a new tool in teaching structural geology. Built by NOVA's uber-clever engineering guru Rob Woodke, this is the Butter Buster. The idea came from Structural Geology of Rocks and Regions by Davis & Reynolds, the text I use for teaching structure, and was recommended as a crowd pleaser by Aaron Martin, the structural geologist at the University of Maryland.

So what's the deal? The deal is that materials like rocks behave differently if they are cold or if they are warm. (They also behave differently if they are under high or low pressure, and if strain is applied quickly or slowly, etc., but here our independent variable was temperature).

We can demonstrate this difference by creating an analogy between rocks and a more familar substance, butter. The butter buster creates a fault/shear zone of adjustable width, and displaces the two ends of the butter in opposite directions. If it's cold, it breaks. If it's warm, it flows. Ta-da!

Check it out...

Cold:


Room temperature:


Warm:

Labels: analogies, books, structure, teaching

Last Saturday was my Field Studies in Geology trip to Shenandoah National Park. Here's a few shots from the day's geologizing...

Garnets in the Pedlar Formation granite gneiss, oldest rock in the park at ~1.1 Ga.


Meta-basalt columns of the Catoctin Formation (photo by Mathina Calliope):


At the end of the trip, I have the students order a series of strips of paper with different geologic events in the park's long geologic history. They have to figure out the proper order based on what they learned that day:





Lastly, a group photo overlooking the Browntown Valley:

Labels: field trips, metamorphism, minerals, national parks, nova, shenandoah, teaching

These videos were shot by NOVA's videoman extraordinaire Richard Attix, who helped me immensely this morning by splicing together these movies for use in my MSSE capstone presentation at the end of next month. Enjoy!

Teaching on the Billy Goat Trail (a blend of instructor-focused lecture and student-focused exploration):

Hiking on the Billy Goat Trail:


End-of-trip activity - "Ordering Geologic Events":

Labels: field trips, nova, piedmont, teaching

Dear readers,

Here's a list of the samples I'd really like to have to show my students examples of the processes we discuss:

• A lava pillow (maybe a pillow basalt). Fresh would be best, so I could show the outer crust of obsidian, and the inner basalt. An ancient pillow would be second best.


• Boudinage. A nice hand sample of boudinage, maybe a granite dike in a shist? Or a sandstone stratum within a shale matrix? I feel like I should already have one of these, but I don't... All the good local examples are too big.


• Flame structures/ball-&-pillow soft sediment deformation.


• A komatiite sample.


• One of these. (Eubrontes track with radiating mudcracks, featured this morning on ReBecca's Dinochick Blogs)

I've been a good boy this year. Anybody got any spares they want to trade for some nice Skolithos-bearing cobbles? (...or something else we've got a local supply of?) I'll pay shipping!

If not, please alert Santa that I'd appreciate him filling my stocking with these goodies,

Callan

Labels: basalt, igneous, primary structures, structure, teaching

This might be a "Words Worth" sort of item...

I find that a certain subset of my students (i.e. the ones who don't do very well in my classes) make no distinction between the phrases "tectonic plates" and "plate tectonics." To me, these mean very different things, but to the undertrained geologist, they must appear synonymous.

What's the difference?

A tectonic plate is a thing, a noun, an object. It is a slab of the Earth's lithosphere that behaves as a relatively coherent block. It is not eternal. It can grow with the addition of new lithospheric material from neighboring plates along its edges (accretion) or fuse with another plate along a suture zone. It can also break apart discretely, as Eastern Africa is doing today, or diffusely, like the Basin and Range province of North America, where the crust is being stretched and thinned.

On the other hand, plate tectonics is a paradigm, a model for how the Earth works. It is a well-corroborated hypothesis that explains so many disparate phenomena it has earned the status of a theory. (And I mean theory in the scientific sense -- a seriously well-founded concept, on par with the theory of gravity, atomic theory, or the theory of evolution by natural selection: these are all hypotheses which have been repeatedly tested over many years and never falsified, so that they are our best working explanation of how a particular thing works.) It is a variety of tectonics in general, which includes non-plate-oriented explanations for building things like mountain belts and continents. Plate tectonics is an idea, an explanation.

Anybody else encountered the false conflation of these two different terms? I think it's going to have to be something that I address up front when I introduce plate tectonics in class, in the manner of A Private Universe -- assessing student worldviews and weeding out (nullifying) false conceptions as a necessary first step before you can sow correct ideas.

Labels: plate tectonics, teaching, words

Hey there Northern Virginia-area readers,

Our readers in Kansas, California, Colorado, London, India, & Australia* can't do what you can do.

Only YOU can sign up for NOVA summer field geology courses.

Check them out. See you out there in the real world.

Sincerely,

Callan

* = representative sample only, chosen for geographic diversity. No slight intended for the many other readers in equally far-flung, equally worthy locations.

Labels: field trips, nova, teaching

Here's question #17 from last week's Environmental Geology final exam:

Which of the following haiku poems best describes the formation of oil?

Swamp plants leaf out green
then die and get squeezed, sans air.
Carbon gets more pure.

Plates skitter about
plastering terranes on front
like trucks with kittens.

Surface magma sweats,
devolatilizes. Its
fluids drop out ore.

Phytoplankton bloom
in sunny water then get
cooked and leak black goo.

Fossil fuels get lit
and oxidize; humans thrive.
Damn that CO2.

Not the most challenging question on the exam, but it was fun to write...

Other geoblogger instructors -- Do you amuse yourself (and your students) by injecting humor into exams? Is this poor form on my part? Is it genius? Weigh in. I'm curious to know whether this habit is ridiculous or common.

Labels: art, humor, teaching

One of my Honors students, Hope W. (author of yesterday's discussion of the Chalk Point Power Plant), kept a tally on Facebook of quips and phrases from this semester's Environmental Geology class. Now that the semester is over, I offer them to the public at large, despite the utter lack of context. Enjoy!


"Imagine how the lava feels."

"Earthlings are made of Earth."

"What do meteorologists study? Hint-- NOT meteors."

"It [the oceanic crust] is like a giant sheet of tissue paper."

[Referring to the continental crust, in comparison to the oceanic crust] "It's light and fluffy, like a souffle."

"We don't know the actual specifics."

"When you go up, you're not going North - you're going away from the Earth."

[Dramatizing the extraction of paleomagnetic data from rocks] "Continent, where was the pole for you 600 million years ago?"

"Oceanic crust is like James Dean and continental crust is like Dick Clark."

"Here's what we know about tectonic plates: some of them are big... some of them are itty-bitty."

"You can't forget Djibouti."

[Referring to the 1811-1812 New Madrid earthquakes] "There was just no one west of that to report how much shaking there was. Or at least no one who spoke English and felt like talking."

"Take my word for it man! I'm a scientist... No, that's not how it works."

"I have a nice layer of peanut butter on my arm."

"The same thing happens with rocks... it just takes longer."

"As continents move along they pick up junk."

"L.A. will end up in the armpit of Alaska."

[Referring to Redoubt] "Drama-queen of a volcano."

[Comparing geologic hazards] "If you use up all your water, then you die and you don't have to experience the earthquake."

"If bamboo collapses and falls on you it doesn't hurt anywhere near as much as brick."

Let me know in the comments if any of these requires an explanation...

Labels: analogies, humor, nova, teaching

Today, I present a guest post from my student Hope W., who described her experiences visiting the Chalk Point Generating Station in Maryland on our Environmental Geology field trip the weekend before last. The essay is posted here with her permission. Enjoy! -CB

The Chalk Point Generating Station is a coal burning power plant owned by the Mirant Corporation. Our guide during our tour was Greg Staggers, the plant manager. There were three main subject areas that Mr. Staggers talked to us about: power generation, the economic supply and demand, and environmental regulations and precautions.

Power Generation:
Mr. Staggers explained how the station has two different types of units. They have steam units and combustion units. Mr. Staggers described how the two different types of units are designed. He said that the steam units are like giant boilers, and that the combustion units are like jet engines. The plant has four steam units and seven combustion units, both types use fossil fuels to produce energy. Mr. Staggers explained how when power is first generated it is at too high of a voltage to be safely used by the public in homes or offices; and how the current has to be run through various lines to transformers and substations in order to be brought down from 20,000 volts (the level generated) to 110-220 volts (the level used in homes and offices.) Mr. Staggers pointed out the transformer field we drove past on the way in on the aerial photograph of the plant explaining that that’s where the process of conversion begins.

In response to Sophia's question about why the plant was built next to the water, Mr. Staggers explained the complex system for using water from the river to cool the equipment in the plant. As he talked in depth about this system he described how ideas improved through time and experience, as well as environmental regulations which lead the plant to finding more efficient and ecological ways of utilizing the river water. Later on when we took our tour through the plant we had the opportunity to see the some pipelines that the river water runs through. The water runs through the pipe-lines to cool the steam that is emitted during the power generation process. When the river water is released back into the river from the plant it has picked up no chemicals, and has only increased in temperature by approximately 20°F.

Mr. Staggers told us about four of the units that get run; units 1 and 2 which are combustion units and units 3 and 4 which are steam units. When running at full capacity units 1 and 2 operate at 90% efficiency, burn 2.5 million pounds of coal per hour, and use 14 megaWatts of the energy produced to operate; and when units 3 and 4 are running at full capacity the burn 650 gallons of oil per minute. Mr. Staggers informed us that the enormous pile of coal we saw on our way in would last for 45 days if the plant were running at full capacity.

Economic Supply and Demand:
In the 1990's the system was deregulated, which basically means that the power generation, wholesaling of the utility, and the supply distribution were all split up. So when the Chalk Point station produces energy they sell it to PJM a 'middleman' who will then sell it to the suppliers like Dominion Power etc. who then sell and distribute the supply to the public. I mentioned the transformer field earlier in this paper in reference to the generation process, but the transformer field has economic implications as well. The transformer field is also where the producers pass of the ownership of the energy to the middleman.

Mr. Staggers explained the bidding system for establishing the market value for each day. In the bidding system if you are over producing you get paid the difference in price from your morning bid in real time. During the tour we got to see the control rooms where the market price rates were being adjusted in real time. In response to Dustin's question about how they know when to produce Mr. Staggers explained how the middle men suppliers make that call based on the morning bids and the actual demand by the public, when the suppliers make the decision about production levels they call the plant to inform them of how much they need to be producing.

In terms of the national economy coal is the cheapest in explicit costs, in equivalent quantities the price for coal is 1/3 that of oil and natural gas prices, which is why more than 50% of the U.S.'s power is generated by coal. In terms of the local economy the Chalk Point station produces a 500 thousand volt ring around D.C. It is estimated that in the next five years 1 million homes will be added to the market that the Chalk Point station caters to.

The demand for coal is influenced by seasonal changes which gives it a cyclical demand. Callan asked if the increased attention on alternative methods of energy has affected the demand for coal in terms of reduction. Mr. Staggers said that no such change has been apparent and that the cyclical trend has followed a predictable pattern.

Environmental Regulations and Precautions:
Mr. Staggers told us about the regulations the plant has been mandated to conform to, as well as what the plant has done of their own accord for the sake of the environment. Some of the changes that the plant made in the past include setting up new stack facilities in 1982 because of environmental regulations. When the clean air act was passed in 1992 brought down their level of pollutants they were releasing into the atmosphere from 1.4 to .7 Further regulations such as; the separated overfire air controls in 2000, selective auto-catalystic reduction in 2007, and selective catalystic reduction in 2008 brought the pollutant rate down to .06. All of the methods above have dropped total output capacity by some amount.

The plant has also put up two boundary nets to protect fish from the areas where hot water is released and two more boundary nets as well as a fine mesh screen to prevent the fish from getting sucked up into the pumps for the cooling system. The plant has many systems in place to reclaim energy where they can to avoid waste, such as how they use residual heat from the coal burning process to heat the incoming air from its current temperature to be closer to the temperature required for being used as an infuser in the combustion process. The plant is in the process of building a "scrubber" which will reduce the sulfur emissions by 98%. The method this "scrubber" will use will allow the plant produce and collect gypsum which the plant will sell for its use in drywall. The plant also has a system set up to collect ash by a precipitation method; the ash collected is also sold for its use in drywall.

The plant has continuous emissions monitors which monitor emission levels of CO2, SO2, and NOx. The data from the monitors is sent quarterly to the State and the E.P.A. In the control room Callan asked a question about the plant's ppm output of CO2. Mr. Staggers said that measure by percentage and he did not know the output in ppm . This discussion lead to a very clear statement by Mr. Staggers that he wasn't convinced that it really made a difference. Mr. Staggers informed us that the plant's output of CO2 is 12% of flue gas volume, which Callan calculated to be 120,000 ppm. From Mr. Staggers' point of view as a producer of a commodity it is hard to see much else besides bottom line explicit costs. This was not his position out of greed, but out of responsibility to keep the company running so he has a job to provide for his family, and his employees as well. On the other hand, scientists cannot escape the implicit costs of CO2 emissions.

There needs to be a level headed discussion in a neutral setting were the two groups can learn to understand each other and start to cooperate. We as individuals and a nation must step up and set the example. When we start working together we will create the safe harbor necessary for understanding and cooperation to grow and flourish.

Labels: coal, energy, environmental, maryland, nova, oil, teaching

Yesterday, I was fortunate enough to be able to tag along on the University of Maryland's petrology field trip, to five locations in Maryland showcasing a variety of igneous and metamorphic rocks. I'd like to thank Rich Walker and Roberta Rudnick for allowing me to come along on the excursion, and UMD graduate student Ryan Kerrigan for alerting me to the trip's interesting rocks in the first place. They have a crew of enthusiastic students, and some cool outcrops!

Our first stop was in northern Maryland's Cecil County. Along the banks of the Susquehanna River, just upstream from the I-95 bridge, is an abandoned quarry of the Port Deposit Tonalite.

Here's Rich and Roberta leading us into the quarry:


UMD students examine the semi-overgrown outcrops of the tonalite:


Tonalites are kind of like granites, except they have only very low amounts of potassium feldspar. This particular tonalite has a magmatic crystallization age of 515 Ma (U/Pb in zircon) and a metamorphic age of 490-480 Ma (Rb/Sr in biotite). Close-up of the rock's texture:


ADDITION: Kim notes in the comments that I didn't draw an explicit connection between the metamorphism and the metamorphic foliation that is so prominent in this photo. She's right: The wavy linear pattern you see in this photo is produced by minerals aligned by differential pressure. Squeeze the rock "top to bottom" and you produce a foliation that runs "left to right."

On the basis of isotopic evidence, the Port Deposit Tonalite is interpreted to have formed as an igneous pluton offshore of ancestral North America, underneath an island arc in the Iapetus Ocean. Later, subduction brought the island arc into contact with North America, triggering the Taconian phase of Appalachian mountain-building.

Here's a closer look at the texture and mineralogy. You can see some k-spar present here, though this was not a common mineral to see at the outcrop...


There were some nice xenoliths present, indicative of the host rock into which the PDT intruded:


Here's a quartz vein cutting through the tonalite. You'll notice that the vein is emplaced approximately perpendicular to foliation, suggesting the same maximum stress which imparted the foliation also extended the rock parallel to the foliation place, opening up fractures that when then fill with the most mobilizable minerals available (in this case, quartz):


If you look closely, you'll see that the fracture which opened up in the tonalite to allow this vein to be emplaced has a ragged edge (not a clean break):


Next up: the Setters Schist...

Labels: appalachians, cambrian, granite, igneous, maryland, metamorphism, ordovician, structure, teaching, xenoliths

Here's the results of a neat little experiment my Environmental Geology students did a couple weeks ago. This is the first time I've run this activity, and I was pleased with the results:

Labels: climate change, CO2, global warming, nova, teaching

When I visited the exposures along newly-minted New Route 55 in West Virginia in March, I was so impressed, I decided to bring my structural geology students there on our trip. Now, after two stops in the Blue Ridge and a late afternoon anticlinorama, we woke, broke camp, and ate some great eggs and sausage (mine were swimming in coffee due to an accident with the French Press, but hey -- it all goes the same place, right Ben?) and set off to the west.

Hanging Rock Anticline roadcut:


Hanging Rock Anticline as viewed from the valley of the Lost River, where Old Route 55 wends and winds:


Ben, Dave, and Joe on the berm (note the thrust fault above their heads):


Plenty of primary structures to be seen here, too, like these trace fossils:


A hand-sample of trace-fossils (Arthrophycus, I think):


...or this beauty:


Small reverse fault with an offset of ~1 meter:


Here's a fossil (??) that I don't understand and cannot identify. I saw four of these out there. Can anyone (Tom, ReBecca?) help me identify this sucker and understand how it formed?










We moved on down the road a bit, to this lovely monocline (Jim & Jay for scale):


John, Karine, & Ryan take a closer look at primary and secondary structures in these strata:


Lovely flute casts:


Plumose structure #1:


Plumose structure #2:


Paleo-river channels incised into these strata (at the time of their deposition):


Reduction "halo" around a carbonaceous plant fragment fossil:


Ripple marks:


More plant fossils (these were the largest I saw):


Lots of carbon films of shredded up plant chunks:


Ball & pillow / flame structures:


Ditto, and note the graded bedding in the upper sandstone layer, too:


Great trip, everyone! Thanks!

Labels: field trips, fossils, primary structures, sediment, structure, teaching, valley and ridge, west virginia

After the Garth Run high-strain zone and a night hanging out by the campfire at Heavenly Acres with the William and Mary Structural Geology class, the second stop on our Structural Geology trip was in Shenandoah National Park, looking at the deformed meta-basalt columns on the Limberlost Trail. Longtime readers of the blog have seen these unique (in my experience) columns before, in a post from last May.

This is an outcrop of the Catoctin Formation, a series of (mainly) basaltic lava flows that erupted sometime older than 565 Ma (only the youngest, rhyolitic layers have been dated, and evidence suggested that significant amounts of time may have passed between the eruption of each stratum of basalt deeper down in the stratigraphic stack). As the lava cooled, it developed cooling fractures that formed perpendicular to the isotherms. These fractures likely initiated at the top and the bottom of the flow, and propagated towards the middle over time.

Later, during Alleghenian mountain-building (~300 Ma to ~250 Ma, roughly), the rocks were subjected to greenschist-facies metamorphism, and were deformed. The basalt's consituent minerals re-equilibrated and reacted to become other minerals, most notably chlorite and epidote (both of which are green).

Here's John and Joe checking out the columns:


Exquisite! Even arrest lines on the side of each column are preserved. In an undeformed basalt column, these arrest lines would be perpendicular to the column edge. Here, they have a pronounced angular relationship, indicating the shearing of the overall column:


Bobby measures the angular shear along the length of the column:




Goofball professor poses with column:


Jay plays the column like an electric guitar:


We found some nice plumose structure too:


Finally, we evaluated the concentric rings of minerals filling amygdules (vesicles that had been infilled with mineral deposits after lithification) in an attempt to determine whether they could be used as strain markers, or whether they may have attained their ellipsoidal shapes due to stretching of the bubbles in the originial lava (i.e. like this) and then been infilled with minerals:




...and then we were off to Field Study Area #3...

Labels: appalachians, basalt, field trips, igneous, metamorphism, national parks, primary structures, proterozoic, shenandoah, structure, teaching

I took my Structural Geology students on a three-day field trip this weekend to examine outcrops in the Blue Ridge and Valley & Ridge geologic provinces. Here's a few photos of the team at our first (of four) field study areas, the Garth Run high-strain zone:

Examining the structure and taking strikes and dips:






Fabric elements cross-cutting one another:


Mylonitic fabric:


Foliation wrapping around a feldspar porphyroclast:


This is kind of interesting: a big pancake (oblate ellipsoid) of blue quartz, with a potassium feldspar in the middle:


And if you zoom in close, you can see that the feldspar porphyroclast is broken in the middle (along the plane of cleavage) with non-blue quartz filling in the gaps:


I think this blue quartz likely formed in the pressure shadow of the resistant feldspar porphyroclast during flattening strain, and eventually that feldspar began to brittlely deform, extending in the direction of minimum principal stress.

Quite a bit of variation across strike:


The students found some nice euhedral garnets too, though this was a block of float from upstream, and not intimately associated with the high-strain zone itself:


More tomorrow, from Field Study Area #2...

Labels: blue ridge, field trips, igneous, metamorphism, structure, teaching, valley and ridge

This fall, Professor of English Joyce Brotton and I will be offering a new linked pair of Honors courses: Her English 244, Survey of English Literature II, will be paired with my Geology 106, Historical Geology. Enrollment is for Honors students or by permission of the instructors only. Both classes will meet in CS 219 on Mondays and Wednesdays. Dr. Brotton will teach from 11:30am-12:45pm, then we'll have a lunch break for 45 minutes. At 1:30pm, I'll pick up with lecture until 2:45pm, and on Wednesdays, we will follow that with lab.

Dr. Brotton and I have collaborated in planning the curriculum, which in the literature half of the class will include readings of Darwin, Lyell, and "A Pair of Blue Eyes" by Thomas Hardy (which features trilobite eyes!). Joyce plans to conclude the literature class with The French Lieutenant's Woman, which attempts to reconcile man's place in a world that science is revealing more and more to be indifferent to man. On the geology end of things, writing the field trip reports will hopefully more of a satisfying practice with an English professor on hand to advise!

Interested NOVA students should contact Dr. Brotton or me for more details.

Labels: nova, teaching

Here's some photos from today's Physical Geology class field trip to the Billy Goat Trail. It actually snowed on us a little bit... cold! My student Luke O'Neil took all of these, hosted on his Facebook page, and this is an experiment to see if I can post Facebook photos on my blog... keeping my fingers crossed...

Migmatite:


Il profesore showing tilted tree trunks (knocked in a downstream direction during floods):


Folded graded bed in metagreywacke:


Students circle around an exotic boulder of the Catoctin Formation greenstone (from the Blue Ridge province); the boulder was transported downstream by the ancestral Potomac River when it was flowing on the Bear Island strath, before incision and abandonment of the former river bottom to become a bedrock terrace:

Labels: field trips, geology, maryland, national parks, nova, piedmont, rivers, teaching

A couple of weeks ago, I did a fun experiment with my Structural Geology class at George Mason University. We injected plaster of Paris liquid into a 2-liter soda bottle full of solidified gelatin to induce a fracture by increasing the pore pressure. These experiments show that the fractures (which geologists call "joints") are elliptical in shape, and bear distinctive structures including hackle fringes which correspond to real structures seen in real rocks. (see previous NOVA Geoblog posts on joints and their distinctive structures)

Here's a video of our first joint, made with a horizontal maximum stress:


Here's a shot of the experimental set-up for the second round, in a bottle with a vertical maximum stress:


Lousy, blurry video of the second experiment:


Low-res shot of the resulting joint surface. Note how it flares to parallel with the side of the bottle due to variations in the stress field, and also the lovely hackle fringe:


A close-up of the hackle fringe where the "joint" (white plaster of Paris) stops and the "rock" (transparent gelatin) begins:


As you can tell from the audio in the YouTube clips, we all found this pretty exciting!

For those who teach geology, this is a relatively simple experimental set-up (although I hate the smell of unsugared gelatin cooking) that is a great visual demo of the relationship between stress orientations and joint orientation, pore pressure, and joint/ vein structures. A big thumbs up from the Bentley classroom!

Labels: structure, teaching

It's my pleasure to inform you that my colleague Ken Rasmussen won this year's John Moss Award for the teaching of geology, as bestowed by the Eastern Section of the National Association of Geoscience Teachers. I nominated Ken, and was supported by nearly a dozen supporting letters from his legions of current and former students, many of whom credit him with launching them on a career in geology. Congratulations, Ken! (and keep it up!)

Labels: nova, teaching

Last week, I updated my field trip photo page with a fresh batch of images from last spring's Field Studies in Geology course to the Billy Goat Trail. Here are the new shots:












All photos are by Kevin Mattingly, NOVA photographer.

Labels: field trips, maryland, nova, piedmont, teaching

An article in today's Kids' Post discusses rock collections.

Hat tip to Brian R!

Labels: dc, minerals, teaching, virginia

I hereby initiate a geoblogosphere meme...

What are ten things that every geology major ought to know about? The only restriction is you're not allowed to list anything that has already been listed by a previous geoblogger. You don't have to list everything, just ten important things.

My ten:

1. The relationship between cooling rate and crystal size in igneous rocks.
2. The fact that rocks can flow, given sufficient temperature and pressure [and low strain rate, for the purists out there].
3. The idea that sedimentary rocks reflect specific depositional settings. By studying modern depositional settings and the sediments they contain, we can interpret ancient sedimentary rocks in light of the conditions under which they accumulated.
4. The fact that the chemical stability of molecular configurations (minerals) changes with different temperatures and pressures (metamorphism).
5. Large Igneous Provinces, and their potential role in tectonics and expressing mantle plumes.
6. Elastic rebound theory for the origin of earthquakes.
7. The notion of partial melting, and its relationship to Bowen's Reaction Series.
8. An understanding of the carbon cycle, and an understanding of the atmospheric physics that facilitate global warming.
9. The role that rivers play in shaping the landscape: nickpoints, terraces, quarrying, abrasion, drilling of potholes, etc.
10. The Earth is 4.6 billion years old, which is extremely old in comparison to human life -- and the reasons we think it's so old [Pb isotopes, etc.].

Please, add to these... So far Mel at Ripples in Sand, Chris at GoodSchist, Eric at The Dynamic Earth , Lockwood at Outside the Interzone, Bryan at In Terra Veritas, Kim at All My Faults..., Garry at Geotripper, and the Short Geologist at Accidental Remediation have added their top tens. Plus, Silver Fox at Looking For Detachment posted 4, and the comments section on this post has another suggestion from Michael Welland (of Through the Sandglass) and others. That's 85 things to know... and counting...

Labels: blogs, geology, teaching

Yesterday, four Honors students and I went out to West Virginia's route 55 (between Wardensville and Moorefield), to look at some sedimentary strata and associated tectonic structures. Our guide was my friend David Dantzler, an enthusiastic amateur geologist. Here's a map of the terrain we traversed:



As you can see, this is part of the Valley & Ridge province, an area of the country defined by Paleozoic rocks that were folded and thrust-faulted during the Alleghenian phase of Appalachian mountain-building. Recently, a new road has been constructed traversing these valleys and ridges. It's a bit of a boondoggle, a pet project of West Virginia senator Robert Byrd which funneled federal dollars into the Mountain State, ostensibly to make it easier for the chicken farmers of Moorefield to get their birdie bits to market on the east coast.

This image ought to give you a sense of the project's scale (big bridge), and how much use it gets (no one on the bridge):


But the U.S. taxpayer's loss is the geologist's gain... There are some pretty spectacular new exposures of Valley & Ridge rocks along the new route 55. Here's the NOVA van parked at an outcrop of Tuscarora Sandstone that is arched up into a broad anticline. Again, notice how few people are driving on route 55 here:


Ooh, look: heavy traffic!


Contact between the lower Tuscarora Sandstone (a Silurian-aged extremely pure quartz sandstone, variably fused to quartzite), and the overlying (darker-colored) formation, which is either the Rose Hill Formation or the Mackenzie Formation at this location:


We found oodles of cool trace fossils:







But it wasn't just sedimentary layers. There were also some cool tectonic structures, like this joint in the Tuscarora, showing a beautifully developed hackle fringe:



Here's some "pencil cleavage" where fine-grained shale develops cleavage that intersects the planes of fissility, causing it to fracture in long slivers:



I slammed on the brakes for this one: an awesome anticline...


I forced David and the students to act out the orientation of the bedding planes at this anticline:


Honors student Jason points out a small thrust fault in the outcrop above him: You can see the offset in a greenish/gray shale layer:


In case it wasn't obvious above, here's a zoomed-in shot, with the offset layer highlighted (the miracles of Photoshop!) and the fault labeled:


We all had a grand day outside, and the rain held off until our return trip, which was pretty great. Thanks to David for showing us these rocks, and thanks to my students for being smart and inquisitive and into field trips.

Labels: appalachians, devonian, field trips, fossils, mountains, nova, politics, primary structures, sediment, silurian, structure, teaching, valley and ridge, west virginia

It's getting to be springtime... and that means field trips!

My first field trip of the semester is tomorrow: my friend David Dantzler has organized a trip to look at stratigraphy and structure out on a new highway in West Virginia. I'm supplying half a dozen Honors students and a NOVA minivan, but David's handling the content. And of course, I'll be on hand to comment on "teachable moments." Looking forward to it.

Other trips upcoming this semester: Billy Goat Trail (x4!), Massanutten Mountain, Old Rag Mountain, Washington DC walking tour, and a weekend-long structural geology trip to the Blue Ridge and Valley & Ridge provinces. I love field trips; really they were the aspect of majoring in geology that appealed to me the most - the fascination with Earth processes took longer to develop.

See you in the field!

Labels: blue ridge, field trips, maryland, nova, piedmont, teaching, valley and ridge, virginia, west virginia

I'm sure I won't be the only one to be writing about this today, but here's a couple of links to news items about Liberty University's "Advanced Creation Studies" students touring the Smithsonian Institution's National Museum of Natural History.

NBC (snarky!)
Washington Post (with photos)

Labels: evolution, museums, news, smithsonian, teaching

In Environmental Geology lab last week, we were playing with dirt... and sand... and gravel... and other granular materials, piling them up to see the angle of repose.

One of my students, Kristen P., brought in little "Monopoly" houses so that her experiments carried a bit more significance...




I thought this was very clever -- it made you "care" more about the angle of repose when someone's "home" was at stake... Good work Kristen!

Labels: humor, mass wasting, nova, teaching

Just got a batch of images from the NOVA photographer, Kevin Mattingly. I particularly like this image of last spring's Field Studies class at the Billy Goat Trail:

Here, we're overlooking the upstream end of Mather Gorge, checking out some ~360 Ma lamprophyre dikes exposed there -- but offset on either side of the river!

Labels: devonian, field trips, national parks, nova, piedmont, teaching

I'd like to congratulate my friend and fellow MSSE candidate Rob Greenberg for being awarded this year's Outstanding Earth Science Teacher award for the state of North Carolina. (Link goes to GSA website where winners are listed; I read about it yesterday in this month's issue of GSA Today.)

Rob's one of the most enthusiastic people I know, and a gifted educator. He loves geology, astronomy, climate, and is a strong environmental advocate to boot! If you have ten years to spare, you can check out the wealth of materials he has online at his instructional website.

Congratulations, Rob!

Labels: environmental, msse, north carolina, teaching

Heh! A gem from Mr. Hrynyshyn.

Labels: blogs, evolution, grants, teaching

Labels: art, earthquakes, faults, teaching

For the second time, I'm distributing paper block models by Martin Schopfer at the Fault Analysis Group at University College Dublin. My experience has been that these little models are really useful for helping non-3D-minded students to visualize the subterranean form of geologic structures.

Labels: art, structure, teaching

Last Friday was the first day of Structural Geology at George Mason University. Though I'm a full-timer at NOVA, GMU talked me into teaching Structure this semester, too. I've done this once before -- my first job out of graduate school, in fact. Then (in 2005), it was very stressful for me, and I'm not sure that I did a very good job. Now, though, I'm much more confident as an instructor, and I feel like I've got a better grasp of some of the essential ideas and techniques: both structural and pedagogical.

For the first day of class, I took a page from Kim of All My Faults Are Stress Related, who recently described a simple but effective "first day of structure" exercise in a post. Inspired by this idea of nurturing structural curiosity right from the start, I gathered up a collection of 36 samples of deformed rocks (plus a few non-deformed ones as "decoys") and laid them out on tables in our classroom:

Most of them were samples from my personal collection, which resides in my office at NOVA, but there were NOVA teaching lab samples too, and I added a few more interesting ones I found at Mason, like this ptygmatic fold in a granite dike:

The instructions to the students were twofold: First, visit each sample and describe it as fully as possible, noting in particular its "structural significance" (which I declined to define more explicitly). Then, once everyone had done that, get together as a whole class and organize these samples into groups based on common features. How many groups? Which features? They had to decide.

I took as my mantra a quote my friend Bridget (a writing instructor at NOVA) found:

"Teaching should be as experimental as writing." -Donald Murray

So I was conducting an educational experiment...

Starting the class in this way felt unfamiliar to me -- everyone "knows" that the first thing you're supposed to do is distribute the syllabus and spell out the gameplan for the semester. Or perhaps start with an introductory lecture. So it was kind of eerie and uncomfortable for me to sit still and quiet off on the side while a roomful of eager students (that I had only just met) went to work.

I sat back and made observations. One student was miming squeezing and stretching rocks with his hands -- "replaying" the stresses that he interpreted must have acted on the rocks to leave behind such structures. (Kim has another post up, just today, about the role of gesturing while teaching and learning geology.) I was pleased when (umprompted by me) they started using supplies like hand lenses, rulers, percentage charts, and hydrochloric acid to quantify the samples' characteristics.

Another student picked up a metaconglomerate with stretched pebbles whose boundaries were somewhat indistinct. His pen moved over the surface of the sample, visually tracing out the place where one stretched pebble stopped, and the next began.

Later, a student set aside a chunk of slate with plumose structure on its surface. With raised eyebrows, he said, "I can't say much about that!" A few minutes later, the sound of stippling resounded in the room as one student sketched a grainy sample.

Periods of quiet work were interrupted periodically with joking commentary. The students in this class (mostly guys) appear to have really bonded with one another during previous geology classes. They are all seniors, with the exception of one geography graduate student. It's good to see that they are comfortable with one another.

During the groupwork portion of the exercise, when the students were organizing the samples into clusters based on shared characteristics, I continued my silent observations. "Let's organize them by stress direction," one student said. "But not fault direction?" asked another. "How about directionality, regardless of what it's direction of," came the reply.

They ended up choosing these titles for their groups: "Slickensides," "Bends and folds," "Smashed together," "Tension," and "Undeformed." It was cool to watch this process play out. I had put out one sample of tension gashes in a limestone (extensional fractures infilled with calcite). The sample was one of the few that I had labelled. That went into the "Tension" group, of course. But what about that other sample with the quartz veins? Was that the same kind of thing? It's a different mineral...

The most classic exchange went like this:

Student 1: "I'm confused."
Student 2: "It [the organizational system] made sense at first."
Student 1: "...Like a lot of organizational systems in geology!"
(laughter)

Finally, once consensus has been achieved, we all walked around to the various piles of rock and I talked in a general sense about the structural importance of each one. The students appeared to be pretty engaged with this discussion: after all, they had invested some serious time in trying to figure these samples out; now they wanted to know what they really meant. My discourse on the samples stretched to about an hour. All told, the whole lab, grouping, and ensuing discussion lasted about three and a half hours. I felt really good about the exercise as a way of generating structural thinking during our first few moments (and hours) of class. I preferred this way of starting class to the traditional approach.

Satisfied that we were off to a good start, I passed out the syllabus.

Labels: igneous, metamorphism, sediment, structure, teaching

Due to a scheduling mishap, this semester I'll be teaching my Environmental Geology lab in the new Science Learning Center in the Schuler Building on NOVA's Annandale campus.

This past Thursday night was our first session in there. Exploring the new facility, I opened up an old-looking refrigerator back in one corner. "What's in here?" I wondered....



Whoa! A bunch of dead birds! These are, no doubt roadkill (or window-kill) samples that are awaiting preparation as 'study skins.' Under professor Walt Bulmer, NOVA has developed a robust collection of study skins to aid in ornithological studies. (I'll have to shoot some photos of those sometime.)

Though I hadn't expected to see a pile of dead birds in the fridge, I soon recovered from the shock. Before converting to geology, I used to study ornithology, and have spent time prepping study skins in the lab at William & Mary (and once, in my dad's basement, with a Sturnus vulgaris that turned out kind of stinky). Returning to my students working on their lab, passing the anatomical models and the physics references, I thought how refreshing it was to be working in a lab utilized by all the sciences.

I guess in retrospect, I should have suspected the fridge's contents when I saw this cartoon taped to the front of the fridge door:

Labels: birdies, humor, nova, teaching

First in a series of blackboard sketches? We'll see...

Labels: art, igneous, teaching

Here's a copy of my presentation last week at the NOVA "Power Up Your Pedagogy" conference, hosted here at the Annandale campus (sponsored by our Center for Excellence in Teaching and Learning). Apparently there were some technical snafus for one (both?) of the scheduled playings of the talk, so I wanted to put it online for anyone who missed it. It's 13:40 in length, available as an .avi file. You'll have to download it to your computer, because I can't figure out how to embed it here.

Other talks from the conference are listed (some with video) on the PUP page on the CETL website.

Labels: blogs, conferences, geology, nova, teaching, tech

School of Rock 2009: Cores, CORKS and Hydrology on the Juan de Fuca Ridge

Dates: 23 June - 5 July 2009

Location: Aboard the JOIDES Resolution from San Diego, CA to Victoria, British Columbia

Application Deadline: Wednesday, 4 February 2009; Limited Space Available

The 2009 School of Rock teacher research expedition is scheduled to begin Tuesday, 23 June, 2009 aboard the recently relaunched 143m JOIDES Resolution. School of Rock 2009 participants will be among the first to work and sail aboard the newly renovated ship.
During School of Rock research experiences, K-12, informal, and undergraduate educators will have daily opportunities to conduct hands-on analyses of sediment and hard-rock cores with scientists and technicians who specialize in IODP research. This year's workshop will focus on how cores and CORKS shed light on the hydrology, geology, and tectonics of the Juan de Fuca plate.

Apply Now - Don't Delay!

For additional information, please contact:
Sharon Cooper, Assistant Education Director, Deep Earth Academy Tel: (202) 787-1632 scooper@oceanleadership.org

Leslie Peart, Education Director, Deep Earth Academy Tel: (202) 787-1603 lpeart@oceanleadership.org

Labels: jobs, teaching, washington

Some geology-oriented terms made the New York Times' annual rundown on buzzwords. It's noteworthy that two of the (non-geological) others on the list (futarchy and edupunk) were coined by Virginia professors.

Labels: news, teaching, virginia, words

Christie asks: What are your top ten geological resolutions for the new year?


For me, the list would include:

1. visiting the Galapagos Islands
2. visiting the high Andes (Cotopaxi, Chimborazo), Ecuador
3. finding a cool outcrop of graded beds in the Martinsburg Formation (late Ordovician turbidites in the Shenandoah Valley of Virginia) that Rick Diecchio told me about last week
4. "walking on the Moho" in Gros Morne National Park, Newfoundland (late summer)
5. seeing Snowball rocks and Ediacarans on the Avalon Peninsula, Newfoundland (late summer)
6. visiting Egg Mountain paleontological site, Montana
7. joining my colleague Ken Rasmussen's field trip to the Culpeper Basin, a Triassic rift valley in northern Virginia
8. some cool trip next winter break (2009-10): perhaps Patagonia? Or Antarctica?

I've also got some big teaching resolutions:

1. Running a successful and robust Structural Geology course for George Mason University (spring semester).
2. Running a successful and innovation Environmental Geology course for NOVA (spring semester).
3. Running a successful and safe Regional Field Geology of the Northern Rocky Mountains course for NOVA (summer semester).
4. Preparing and running a successful and groundbreaking Honors Historical Geology course linked with English Literature 242 at NOVA, where the English professor and I will bridge the two subjects with readings of Lyell, Darwin, "A Pair of Blue Eyes," and others (fall semester).

On other topics:

1. Finish my M.S.S.E. degree (July)
2. Buy a house
3. Put together a series of geology 'vodcasts' on local geology
4. Write a few freelance articles
5. Publish one cartoon per month in EARTH
6. Prepping (cutting and polishing) a backlog of rock samples from all over the place
7. Successfully moving the geology department into our new building

Labels: canada, ecuador, geology, msse, newfoundland, nova, south america, teaching, travel, valley and ridge, virginia

Two of my bestest students got me this card for my birthday last week:

Labels: art, geologic time, humor, teaching

The current issue of Newsweek features an article that quotes NOVA President Bob Templin on how more students are signing up for classes at community colleges like NOVA, just at the same time the state is cutting our funding.

Labels: news, nova, politics, teaching

Quick quiz!

What does this...


...have to do with this?


A mineral's habit is the shape that a crystal of that mineral will attain if it gets the chance. When most people hear the word "crystal," the image that comes to mind is of a mineral crystal that has attained its full habit. However, most crystals aren't that pretty. If there aren't enough elemental ingredients, or if there isn't enough time to grow nice and big, or if there are other crystals in the way, then you won't get a nice, sexy crystal. Instead, the mineral crystal's internal structure will fill in whatever space it can, and that will determine its shape. The lower image shows a cartoon of a thin section of rock. In it, you can see a mineral with a "hexagonal" habit, but this actual crystal's shape is jagged and irregular, as dictated by the space available to grow. Most mineral crystals are like this: stunted and "misshapen" as a result of their circumstances.

And that brings us back to the upper image... the square watermelons. As everyone knows, watermelons are approximately ellipsoidal in shape, if given the chance to grow into their full "habit." However, that ellipsoidal shape is tough to cram into a small fridge; it occupies a larger space than its bulk actually takes up. There's a lot of wasted fridge space in the areas adjacent to it. In Japan, a solution has been developed: grow the melons in boxes, so that they are forced to take on a square or rectangular shape. Then, when mature, Japanese consumers can put the square melons in the fridge, confident that no space is being wasted: the melon is taking up almost all of the fridge volume given over to its storage!

Like most minerals, the Japanese watermelons are constrained by their circumstances to grow into shapes that they wouldn't attain on their own.
____________________________
Image sources:
Japanese watermelons - Oddee.com
Thin section cartoon - me, redrawn from a figure in Marshak, 2006.

Labels: analogies, art, japan, minerals, teaching

Here's how I explain the carving of horns as erosional features of glacier geomorphology:








Once you've scooped into the pint of ice cream and out (away from the frozen core towards the thawed exterior), you end up leaving a pinnacle in the middle with curved facets ("cirques"):


... Kinda like this:

Labels: analogies, geology, glacial landforms, teaching

Second in my "ductile flow in everyday objects" series... Ultimately the goal of posting these photos is to develop a repository of teaching images for familiar substances which flow when conditions of temperature and pressure are sufficient.

Here's a plastic cat-food dish (originally square) which deformed in a ductile fashion after going through the heat-dry cycle on a kitchen dishwasher:


Note how the dish has "sagged" around one of the dish rack's supporting bars, like a damp cloth draped over a stick.

Now that it has cooled, it can be removed and show how much it has deviated from its original shape (how much it has strained):

Labels: analogies, structure, teaching

Rocks flow when conditions are right. At the introductory level, many students exhibit an initial tendency to resist the idea of something they "know" is hard and brittle acting in any other way. Faulting, they get. Shear zones... not so much. I find analogies useful in communicating the behavior of rocks at depth, like mylonites. Often I invoke wax, which can be cold & brittle, hot & ductile, or molten.

But I reckon it's instructive to have other clear indications of ductile flow: everyday objects that have flowed under stress.

Today, I offer the first in what I hope will eventually build into a longer series: everyday examples of ductile flow. We begin with a cassette tape left in a hot car (viewed through the back window, which is why the photo is so lousy):

Even the relative moderate stress of leaning on the seat cushion was sufficient to bend this cassette tape, provided it had attained the right temperature (which it's easy to do in the Virginia summer time in a closed automobile).

Anyone else have examples of everyday examples of ductile flow?

Labels: analogies, structure, teaching

It's that time of the semester, when the field trips are over, and the field trip essays start rolling in. These papers I assign are intended to be syntheses of the field trips I take my students on. I want them to interpret the landscape as a geologist would, and support each claim about geologic events in the past with supporting evidence observed or discussed on the trip.

I offer my students the opportunity to submit a rough draft of their field trip paper, and then I give them feedback about both content and formatting/writing style, so they have a chance to revise before submitting a final draft. Each semester, about a quarter of the students avail themselves of this opportunity for feedback before the "real" paper is due. Giving them quality feedback is a time-consuming process, but I feel it's important both to cement geologic concepts in their minds, and to guide them in developing their writing skills.

Accordingly, it's been a slow week for posting on this blog. I've been too busy with work. However, this morning it occurred to me that I could capitalize on my grading efforts by sharing a student essay with you all, edits and all. Why do I think you'll be interested in such a thing? (A) I think it gives some insight into the practice of teaching geology at the introductory college level, and (B) I think this is an excellent rough draft for an essay about Washington, DC's geologic history. The student's name, of course, has been redacted:

Labels: cretaceous, dc, geology, nova, ordovician, teaching

A couple of weeks ago, I mentioned AGI's Image Bank, and to illustrate it I picked three photos by Marli Miller (at the University of Oregon). Dr. Miller has written me and shared a link to a website she has put together to share high-resolution images of geological features and processes. Educators have permission to download the photos for teaching (non-commercial) use. And everyone can benefit from visiting to check out the many gorgeous images there.

Labels: art, teaching, websites

Last week was field trip week for me. I led trips to the Billy Goat Trail on Tuesday and Thursday, and to Washington, DC, on Saturday.

On the Physical Geology field trip to the Billy Goat Trail, we saw rocks like amphibolite, metagraywacke, and migmatite:







Hope and Ana checking out the migmatite:


The group poses with the migmatite, to show how close anatexis is to their hearts...


Jane examines lamprophyre in a weathered-out dike:


Noting the characteristics of metagraywacke:




Traversing 'Pothole Alley'... Joel looks chilly...


Our lunch spot... Alex pretends to dive into the Potomac River...


Traversing 'The Traverse':


On the Historical Geology field trip to DC on Saturday, we were amused to find a jack-o-lantern that had facial hair resembling mine...



But that's not all! We also saw some geology. While you can get a more complete picture at my "DC Rocks" webpage, I'll post a few new photos of new outcrops here...

Here's a nice slab of granite (very angular) set in metagraywacke matrix (metamorphosed accretionary wedge complex)...


Here's two members of the Georgetown Intrusive Suite, showing the (earlier) gabbro stoping xenoliths into the (later) granite:


I love field trips. I love seeing my students light up at being outside, at getting a handle on the stuff we talk about all semester in class. I think field trips are super duper important.

Labels: dc, field trips, granite, igneous, maryland, metamorphism, nova, piedmont, teaching, xenoliths

At work last week, I gave a bunch of exams. Historical Geology took their midterm, and both classes (Historical + Physical) took their lab practical exams. One of the essay questions on the Historical Geology midterm was about evolution. I specifically asked "what is the logic behind and evidence for Charles Darwin's theory of evolution by natural selection?" And while some of the responses I got where excellent (and some were lousy), a large number used the phrase "survival of the fittest," which I never use when explaining evolution. My reasoning for avoiding it is that is an oversimiplification, and not a full explanation. It's almost always more complicated than that.

Curious about whether it was explicitly used in the textbook, I skimmed through the chapter dealing with evolution, and found one instance where it said "... surival of the more fit." But that's not what the students were saying, and tellingly, the ones who used it were not using the phrase as part of a larger, lucid explanation of natural selection's workings. It was more of a placeholder for an actual explanation.

I think where they're getting it is pre-existing ideas about evolution, unrelated to the content I provide in this course of study. It's a phrase, a simplistic platitude, that's already in their heads when they sign up for my course, and I'm failing them by failing to discover it and then debunk it when we cover that topic.

I followed up a bit on that and did a count. 12 students did not use the phrase "survival of the fittest" in their essays, with an average score of 3.29 out of 5 possible points. Eight students did use the phrase in their essays, with an average score of 2.75 out of 5 possible. This is interesting to me: those students that used the cliche' "survival of the fittest" did WORSE than the students who didn't use it. There were four tests that scored a perfect 5/5, and none of them used "survival of the fittest." Of the four students who scored 4/5 (the next highest score), three didn't use the phrase, and one did. Interesting, eh?

I think this is exactly what the PBS program A Private Universe and ensuing series Minds of Our Own were getting at. (I blogged about them here.) It's all about identifying students' misconceptions, and then working to disassemble those misconceptions, and show students how the misconceptions are wrong or incomplete, and THEN building up new knowledge. This "survival of the fittest" business has convinced me it's very important to probe for students' pre-existing ideas before I teach a lesson.

Thoughts?

Labels: evolution, teaching

This weekend, I spent three days on an extended field trip down to southwestern Virginia with NOVA adjunct geology instructor Chris Khourey and four of my Honors students. We left Annandale on Friday morning, and made our first stop at Willis Mountain, Virginia, site of one of the most productive kyanite mines in the world.

Here's a Google Map of the mountain:


The Kyanite Mining Corporation was very gracious in hosting us. I'd particularly like to thank Mike Morris, who took two hours out of his day to show us the site and the mining operation.

Why mine kyanite? It's used as a refractory mineral: that is, one that won't melt under high temperatures. A lot of their kyanite is heated in kilns to produce a second mineral, mullite. The mullite is even more stable than kyanite in high temperature refractory situations. (It won't melt until it hits over 1800 degrees C!) Additionally, they cleverly saw up big blocks into dimensional stone for countertops and the like.

The kyanite mined at Willis Mountain is in a quartzite which also includes a fair amount of pyrite and hematite. We heard about the different procedures used to extract the non-kyanite minerals so that their end product is relatively pure and of constant quality.

Here's Mike showing the overall anticlinal shape of the deposit:

It's a plunging anticline, as you can probably make out from the Google Map terrain view up top.

Some of the dimensional stone, which I think is pretty spectacular:


Close up of the kyanite (light blue, on left) in the dimensional stone.


Nearby Baker Mountain also hosts kyanite deposits, which show a deeper blue color (Mike wasn't sure why, but suggested that chromium may be responsible):


Inside a huge storage building where the mullite (white powder at our feet) is stored:


Atop Willis Mountain itself, showing the weathered kyanite quartzite exposed there:


Honors students ask questions of Mike:


Mike and Chris standing near some fresh boulders of kyanite quartzite:


It wasn't all metamorphism and mining... I also noticed these nice raindrop impressions in a drying mud puddle:


After lunch atop the mountain, we hopped back in the van and hightailed it for southwestern Virginia, on our way to the Virginia Geological Field Conference. More on that tomorrow.

Thanks again to Mike and the good folks at the Kyanite Mining Corporation for hosting our visit!

Labels: conferences, economics, field trips, metamorphism, minerals, nova, piedmont, teaching, virginia

Tuesday, I asked for my fellow geo-bloggers' favorite analogies, with a promise that I would share mine in 48 hours. The time of revelation is nigh... Here are a few of my favorite "geo-nalogies":

The continental crust is high-proof liquor
I see partial melting as a kind of distillation. Just as "sour mash" can be distilled to concentrate the alcohol it contains (separating it from the water it's dispersed in), so too can partial melting act as a "distillation" of the silicate earth. The minerals with the lowest melting temperatures will melt, leaving behind a solid residue enriched in Fe, Mg, Mn, and Ca, and yielding a magma that is enriched in Si, K, Na, and O. With its~granitic composition, the continental crust is 80-proof Jack Daniels. Where did it come from? It's distilled from the sour mash we call "the mantle":

Rocks are cookies
I love a good chunky cookie. Save your Oreos and Lorna Doones for yourself. What I really like is one of those cookies with chocolate chips, oatmeal flakes, raisins, macadamia nuts, and those sinfully good butterscotch chips. What I like about these cookies is not so much how they taste, but how I can tell the difference between the individual ingredients and the cookie they comprise. I use this analogy early on in Physical Geology to illuminate the difference between minerals and the rocks that the minerals comprise:

Continents are old sofas
Like many of us, I had an old sofa in college. The sofa was ripped, had been scratched by a cat, and had coffee spilled on it. It was draped in several layers of blanket in an attempt to cover up the lousy state of the upholstery. Someone added a pillow to the sofa at some point. When I was working for the C&O Canal National Historical Park (translating their geologic history into non-geology-speak), it struck me that the North American continent* was kind of like that old sofa. It had been scratched by glaciers instead of cats, and lava had been spilled on it kind of like that errant French Roast. It had rift valleys, but unlike the sofa's, North America's rifts didn't have springs poking out. New material had been added in the form of exotic terranes, kind of like that pillow got added to the sofa. And the blankets draping parts of the continent were made of sediment instead of fabric... but essentially the two were alike:

*Yes, I know that's the outline of the contiguous 48 United States, not North America the continent. So shoot me.

Tectonic plates are UFOs
In cross-section, a tectonic plate could be seen to have a profile kind of like a flying saucer. The thick part in the middle is the continental crust, but then it has a thin fringe encircling it (the oceanic crust). You can hardly blame a visiting Martian for feeling kind of attracted to it:

The Washington Monument shows geologic time
I didn't come up with this one... But read it somewhere (McPhee, maybe?) that I have since forgotten. Anyhow, the basic idea is that the Washington Monument's obelisk here in Washington, DC can show the difference between the Precambrian portion of geologic time (most of the monument, 88% of Earth history) and the Phanerozoic eon (post-Cambrian, 12% of Earth history). The little pyramid-shaped bit on top is the Phanerozoic. The thickness of a single sheet of paper draped on top of the tippy-top would represent the entire span of human history:

Okay, that's all I've got for today. What have YOU got?

Labels: analogies, geologic time, geology, granite, minerals, teaching

Just a reminder that I'm curious to know which analogies my fellow geobloggers prefer to communicate various geologic concepts. At 4:30pm today, I'll post mine.

Labels: blogs, geology, teaching

Hey geobloggers,

What are some of your favorite analogies for explaining geological concepts to other people?

I'd like to share a few of mine, but I'll wait a couple days so other folks have a chance to chime in. Let's make this something between a meme and an accretionary wedge... I'll set the "deadline" as 48 hours from now... Thursday afternoon, east coast time. (But of course, it wouldn't really matter if you were "late"...)

Maybe publish a post and then link to it in the comments section here?

C

Labels: geology, teaching

Over the past couple of weeks, I've watched a number of videos that readers of this blog may be interested in. Yesterday, I blogged about A Private Universe and Minds of Our Own. Let me mention a few others today.

The Life of Mammals is a BBC production by the great David Attenborough, who also made Life of Birds, Life in the Freezer, Trials of Life, etc. etc. etc. (Attenborough has been making nature documentaries for the BBC since the late Miocene.) If you're into geology as part of a larger natural system, or if you happen to be a mammal yourself, this is a series well worth watching. Attenborough has a signature style involving showing up in different corners of the Earth, and carrying on a continuous narration the whole time. One moment he's in Tasmania, the next in Brazil, but his thought process is uninterrupted. The discussion is of the highest quality, without being too technical. He's got a real gift for this business. Five stars.

I also watched Walking with Prehistoric Beasts, from the Discovery Channel. It's about past creatures; Cenozoic mammals and birds. Because the animals it describes are extinct, it can't have footage of the narrator (Kenneth Branagh) strolling amongst the entelodonts or Andrewsarchus. Instead, they've used puppets and lots of computer generated animation to depict their subject. They're pretty clever about this, using "film" techniques that give it the flavor or an actual nature documentary: They mimic night-vision footage, for instance, as well as "handheld" camera shakiness, herds fleeing an overhead "helicopter" perspective, and the subjects nosing up to the "camera lens." While the animals they describe are quite interesting, I found the production to be a bit on the bombastic side, with pounding music intended to raise the viewers' adrenaline levels during a hunt scene, and so on. All told, the content wasn't as good as Life of Mammals, but I appreciated the way they handled the production, so I'd give it 3.5 stars.

Labels: critters, fossils, mammals, movies, teaching, tv

Another upcoming event that may be of interest to DC-area readers of this blog:

Labels: astronomy, evolution, teaching, virginia

I must recommend a couple of videos to any science educators out there. (I just watched the last of them last night.)

A Private Universe was an eye-opening half-hour video that was followed by a short series called Minds of Our Own. (Links go to video on demand from Annenberg Public Media.) Both titles follow a similar format, and pursue similar content. Their subject is the difficulty in getting students to learn science. Both videos make the hypothesis that the major obstacle in science education is not complexity, or abstract reasoning, but pre-existing ideas about the way the world works. Students come into our classrooms with certain notions, and unless we teachers (a) know what those notions are and (b) explicitly confront them, then the students' natural reaction is to stick with their perfectly-reasonable ideas about the way the world works (and reject the scientifically valid ideas about the way the world works).

A Private Universe opens with a scene of Harvard's graduation, and the filmmakers interview the gowned students about the phases of the moon. Full moon, half moon, new moon, half moon again... Why does the moon have phases. Everyone shown indicates they think that it's the shadow of the Earth on the moon that give it its phases. In Minds of Our Own, similarly shocking scenes unfold wherein the graduates of MIT can't use a battery and wire to light a lightbulb, and again where Harvard graduates are tested, this time on the subject of trees. A tiny seed grows into a massive tree: where does all that weight come from? All those interviewed thought the tree's mass came from the soil (as opposed to CO2 in the air). It's really something to see -- some of the brightest students in the country, demonstrating a basic scientific illiteracy.
Subsequent one-on-one interviews with elementary, middle, and high school students probe for deeper understanding of just what these students think is going on. Some of these interviews yield bizarre interpretations of reality so that the student can match their erroneous worldview with their well-developed logic and reasoning. It's quite striking to see the lengths they will stretch their minds to, in order to accomodate their pre-conceived notions. A Harvard education professor (Philip M. Sadler) who is interviewed in the films says "The most important thing we can do as teachers is find out what our students already think when they walk into the classroom" (paraphrase). You can be an extremely skilled intstructor, in other words, but this basic step is essential. If you don't assess your students' understanding before you teach them, you're setting them up for failure. Students must be confronted with their false views and shown why they are false, if they are to open their minds to other possibilities.

One of the most gratifying scenes is when a young man is explaining why pressure increases in a closed piston. At first, he thinks that because the volume is less when the piston is compressed, it must contain less air. But as he's illustrating this notion, and being asked clarifying questions from the interviewer, you can see him realize that the same number of air particles must be in the piston when it is both extended and compressed: they're just closer together when it's compressed!

From the perspective of an educator, the depressing side of this realization is that we have nowhere near the amount of time it would take to have one-on-one conversations with every student to explore their misperceptions and then gently lead them through a line of logical inquiry to correct those ideas. That takes some serious time. Is there a more efficient way to root out these ideas? I'm not sure.

Has anyone else seen these videos? I was very impressed. Now I'm wondering how best to incorporate this new perspective into my own teaching...

Thanks very much to Nicole LaDue (NSF) for sending a DVD of these videos my way.

Labels: astronomy, movies, plants, teaching, tv

Hey there! Do you (a) live in the DC metro area, (b) have an MS or a PhD in geology, and (c) want to teach? Well, NOVA might have a job for you. We encourage qualified applicants to send a c.v. and a brief letter of interest to Assistant Dean Craig Jensen at cjensen@nvcc.edu. Mainly we're recruiting for next semester, but we also had an instructor bail out on us this semester, so there is in fact a Monday/Wednesday afternoon class which will have to be cancelled unless we find someone ASAP.

Labels: geology, jobs, nova, teaching

When I look back on my four years of undergraduate geology education, the one thing that strikes me as the most important thing I learned is the age of the Earth. It sent my mind reeling to recognize what a huge old planet I was on, and how ephemeral was my own species' time on it. I was a blip, a temporary arrangement of carbon, hydrogen, oxygen, and a handful of other elements that would last a while, and then disassociate. Material and energy passed into me, and out. This kinetic chemical phenomenon known as me would soon pass, and the Earth would keep turning. The human species would reach its zenith, then collapse (or evolve into something else), and the Earth would keep turning. The continents would rift and crash and the map of the Earth would soon be obselete, and the Earth would keep on turning. Climates change, meteors hit, "rivers shift, oceans fall, and mountains drift" (REM, 1985), and still the planet keeps on spinning, keeps on orbiting, keeps on keeping on.

The day I really realized the age of the Earth wasn't the day I heard "4.6 billion" in lecture. It was the day I sat there studying and grasped it internally -- it clicked that it was immensely, unimaginably old. My temporary human mind was a short-time-scale phenomenon, and it was impossible for this small cerebral system to get a grip on the true scale of the planet's age. While I would never really know (comprehend/appreciate) the age of my planet, I tapped into something fundamental that day. Looking back on it now, I'm reminded of John Playfair's words when his pal James Hutton took him to Siccar Point for the first time: "The mind seemed to grow giddy by looking so far into the abyss of time" (1805).

When I made that cognitive leap (by essentially realizing it was impossible for me to fully make the cognitive leap), I got stuck on geology. I connected to the study in a way I hadn't done before. Suddenly I was subject to a dizzying temporal vertigo, as if a layer of flooring had crumbled away leaving me gazing into a bottomless pit. The realization gave a whole new perspective on things, and it was exhilarating. It felt like one of the conversations when you're getting to know someone, and realizing that they are both intriguing and yet never completely knowable. It draws you in, connects you. Without getting too gushy, it's kind of like falling in love. I've been a geologist ever since.

As I learned more, both in school and on later peregrinations around the world, I found that geology was a great traveling companion. No matter where I went, geology was there with me, showing me new things, giving me insightful perspective. I was looking at the world through geology-colored glasses, and finding that it had a lot to show me. The world made more sense on an elemental level. Hills made sense; rivers made sense; mountains made sense. While I couldn't claim to fully understand any of these phenomena, I could claim a connection to them now that wasn't there before. They were no longer random in my mind; they had a place in the overall system, and it took geology to make me realize it.

So this perspective has stuck with me, and it's what inspired me to pitch "geology as a connector" as this month's Accretionary Wedge theme. (Newbies: the Wedge is a semi-monthly geoblogosphere carnival wherein different geobloggers contribute posts organized around a central theme.) I was curious about what I would get, and I didn't want to restrict my peers' submissions by specifying what kind of connections should be written about.

Sure enough, different people interpreted connection differently. Tromping around in the mountains doing geologic mapping yields more than insights into local structure and stratigraphy, as BrianR of Clastic Detritus discusses how his field work has connected him to the messy reality that is nature.

Jess at Magma Cum Laude is starting her first semester as a graduate T.A., and is going to employ a teaching technique that connected her to the pervasive nature of geology: everything that the Earth puts out for the purpose of assembling Oreo cookies. Something as simple as an Oreo can be the vehicle through which students realize the manifold ways they depend on the Earth every day.

Where are the boundaries between sciences? Is geology a subset of environmental science, or physics? Or both? How do we define the different parts of Nature that we study? Using a Venn diagram, Hypocentre at Hypo-theses explores the connections between geology and other sciences, particularly in the environmental realm.

Similarly, Mel uses a diagram to explore connections in her post at Ripples in Sand. How does geology connect to paleontology? Join Mel in looking at the taphonomic bridge. (And wish her congratulations on her wedding while you're at it!)

Joining the crowd in her first Accretionary Wedge post, A Life Long Scholar (at The Musings of a Life-Long Scholar) makes a connection between the very small and the very large. In trying to answer questions about massive tectonic plates, sometimes geologists must turn to little bundles of mass a few micrometers across. Check out her post to see how garnets can reveal the secret histories of the continents.

And then there are the personal connections. In Looking for Detachment, Silver Fox was the first one to submit a post on the "connection" theme with her description of how different members of the mining and exploration community connect to one another over time and space (Nevada, of course). How do Charles Manson, Kevin Bacon, and exploration geologists all fit together? Read her post to find out.

MJC Rocks of the Geotripper blog has contributed a real treat: an exploration of the connection of geologists teaching geologists through time. It turns out that his academic lineage goes all the way back to Agassiz and Cuvier! A pretty impressive consideration which will surely inspire the rest of us to investigate our own geologic pedigrees.

Finally, over at Harmonic Tremors, Julian shares a story of how his knowledge of geology led him to make a personal connection with one of his cinematic idols, director Brad Bird. If you've seen the Incredibles, you're familiar with Bird's high quality entertainment. When Julian heard that Bird was working on a movie called 1906 about the great San Francisco Earthquake, he wrote a letter to clear up some inconsistencies in the book upon which the movie is based. The talented director took the time to write back to Julian, thanking him for the "seismic tutorial."

Enjoy the various and sundry posts -- follow these digital connections to other geologists in other parts of the world, and feel connected to the larger community of earth scientists. Thanks to everyone who contributed. If I've missed anyone or if anyone wants to submit a late post, give me a shout or post a link in the comments.
________________________
References:
Playfair, John (1805). Transactions of the Royal Society of Edinburgh, vol. V, pt. III.
REM, (1985). "Feeling Gravity's Pull," Fables Of The Reconstruction, IRS records.

Labels: blogs, earthquakes, field trips, geology, metamorphism, minerals, mining, movies, plate tectonics, teaching

My Field Studies in Geology students are required to write papers about the different outcrops we visit. Occasionally, about once per class, they write really brilliant things. Here's a quote that student Brenda used in her recent Shenandoah National Park paper:

Labels: field trips, teaching

Picking up where I left off yesterday, in describing Saturday's field trip out to western Maryland:

2:20pm: We exit Interstate 68 and go south on a dirt road for about ten or twelve miles. This road takes us through the Green Ridge State Forest, and I can tell the students are wary of it. I love a good dirt road, and this one even shows outcrops in the road surface -- resistant sedimentary layers tracing across its rutted, potholed surface. The sun comes out, and I roll down the window, relieved that the weather has finally broken.

3:00pm: We arrive at the C&O Canal's Paw Paw Tunnel, in Maryland just north of the Potomac River and the town of Paw Paw, West Virginia. ("Paw paw" is a native tree in the custard apple family with a lovely fruit also called a paw paw. They're delicious, if you can find one the raccoons haven't already claimed.) Paw Paw is the site of the most pronounced entrenched meanders seen along the length of the Potomac River. These exaggerated loops suggest an old age river system, but they are "locked" at the bottom of deep canyons, which suggests a young river system. The usual interpretation is that the Potomac is a rejuvenated river system: it was "old age," equilibrated to base level and meandering actively, but then base level dropped and it incised to a deeper level, maintaining the meandering shape even though the meanders no longer actively squiggle from side to side.

3:10pm: At the upstream end of the tunnel, we discuss the Brallier Shale (Devonian), and note the angle of the bedding here, which is tipped into the Canal's valley: ideal for landslides. When C&O Canal engineers came to the Paw Paw Bends, they faced a tough choice: construct the canal to parallel the river around its multiple entrenched meanders, or carve a tunnel through a mountain made of this stuff. They opted for the tunnel, saving 6.5 miles of Canal length, but the digging of the tunnel took 14 years!



Because the weather is good, we decide to hike over the mountain first and then walk through the tunnel on the return trip. The hike gives us views of some of the meanders' loopy shapes:



We don't see a whole lot else on the hike, but it feels good to stretch the legs.

4:oopm: We reach the Tunnel Hollow, a long linear valley on the downstream side of the tunnel. Signs of the morning's torrential rains are everywhere in the form of increased runoff. For instance, we see a large stream emerging from the base of a talus slope, flowing across the path and into the canal:



Heading up the Tunnel Hollow, we are greeted with the sight of numerous waterfalls arcing down into the valley:





Here, the layers of the Brallier Formation dip into the Tunnel Hollow, again presenting the potential for slip between the layers, and suddenly big slabs of rock dropping down into the valley. We note the "pins" holding these unstable sheets of rock in place:



4:20pm: My favorite thing about the Tunnel Hollow is the world class exposures of slickensides there. During Alleghenian mountain-building, these sheets of shale slid over one another, as a deck of cards will buckle when squeezed. Sliding between the layers ground grooves into the rock face, and also deposited mineral fibers alligned in the direction of sliding.





4:40pm: Lastly, we got to the downstream end of the Paw Paw Tunnel itself, where multiple waterfalls were cascading down onto the towpath. A fine mist fills the air, and catches the beams of sunlight. There's a nice anticline exposed just above the tunnel archway, and usually I have students climb up the stairs (on the left) to check it out up close. However, today a waterfall was landing on the stairs!







Four of us decided to go for it anyhow, just for the thrill of passing through a waterfall. Several (smarter) students who chose to stay down below pulled out their video cameras and recorded parts of our folly. Here's one showing the climb: (Unfortunately it's both silent and taken "sideways" and I'm not video-savvy enough to know how to fix it in either regard.)



Here's another video of the four of us (Nicole, Jan, Dave, and me) up on top:



4:35pm: Time to enter the tunnel. Flashlights come out, and we begin to walk through the Paw Paw Tunnel. It's a remarkable feat of engineering. It's 3/5 of a mile long, and pitch black. We walk along the towpath, where mules once pulled barges up and down the C&O Canal. It's nice and cool in there, like a cave.

5:10pm: We load up in the vans and depart the Paw Paw Tunnel. It takes a full two hours to drive back to Annandale, so we get rolling. We cross West Virginia, and then work our way east across Virginia. Several students nod off, while others discuss geology and travel along the way.

7:12pm: We return to the Annandale campus. Adios, estudiantes! The NSF crowd (Michelle and Nicole) and I retire to the Auld Shebeen in Fairfax for some Boddington's and Gaelic tunes. It's been a long day; we've covered a lot of ground and seen some cool stuff. Time for a pint!

As with yesterday's post, all photos are by Nicole LaDue, NSF. Thanks, Nicole!
Videos are courtesy of Amy Bertsch and Dean Kauffmann.

Labels: field trips, maryland, stratigraphy, structure, teaching, valley and ridge

On Saturday, I took a group of NOVA summer school students to Shenandoah National Park to look at some rocks. We had great weather, and saw evidence of Grenvillian mountain building, the breakup of Rodinia, and the transgression of the Sauk Sea. A real crowd-pleaser was an outcrop of what was once columnar basalt (the Catoctin Formation). I say "was once" because the basalt has been metamorphosed to greenstone, and the columns have been squashed into more lathe-like shapes.

Here's a few photos of the columns:

All four photos by Nicole LaDue (NSF). Thanks Nicole!

Labels: blue ridge, field trips, primary structures, shenandoah, teaching

Yesterday, I took my Audubon Society / USDA Grad School "Natural History Field Studies" students on a field trip to examine the bedrock geology of Washington, DC. We had a good time: beautiful weather, great attitudes, and even luck with parking! I guess because it's Memorial Day weekend, a lot of people have left town. One of the great challenges of urban geologizing is finding room for those infernal cars...

Here's a photo of the group at Chain Bridge, DC, on Sunday morning:

That class ends on Monday night, bridging the gap between my NOVA spring and summer semesters. It's been a good run -- thanks, folks!

Labels: dc, field trips, piedmont, teaching

I reckon I'm due for a rant. Here's a list of words that bug me:

Dolomite in place of dolostone: dolomite is a mineral. A huge pervasive second use of the word, however, is to mean a rock made mainly of the mineral dolomite, for which the proper name is dolostone. This is so, so, so common it's hardly noticed. And it's so incorrect. Rocks and minerals are not the same thing.

Orogen in place of mountain belt: the word orogen is technically correct, and quite accurate, but in spoken speech, it sounds too much like "origin," and its use can sow confusion. The only real difference I am able to hear when people say "orogen" is that they tend to pronounce all three syllables, while "origin" is generally pronounced with just two: ore-gin. But maybe that's just the Virginians I hang around with. Mountain belt has the same meaning, but I guess it has problems of its own, since mountain belts may not be topographically mountainous any more. Hmmm. ...Toughie.

Extra-syllable words: Should we say benthonic when benthic means the same thing but with one fewer syllable? What about people orientating themselves instead of orienting themselves? What advantage do these extra syllables provide? Are they vestigial structures in our language?

An educational peeve is that students regularly refer to teachers giving grades. I don't know about the other professors, teachers, and instructors out there, but this one really rankles me. My students earn their grades. What I do is keep track of what they have earned, and eventually assign the proper grade to them. I am merely a secretary, an accountant. I tally it up, but the points they accrue (or don't) depends on them. No gifts required!

A huge bummer is the continued use of theory in non-scientific circles to mean hypothesis. In general use, "theory" has a tenuous, shaky implication, while in science it means "as solid and dependable as an explanation gets." David Quammen explored this well in his discussion of evolution in National Geographic a couple years ago. For the record: a hypothesis is a possible explanation of a phenomenon, calling to be tested. A theory is a well-corroborated hypothesis (i.e. it has passed a great many tests) that coherently unites a number of disparate phenomena under one central explanatory umbrella. Big difference there; huge. Makes communication about important concepts difficult.

Lastly, my all-time least favorite word: Believe.

Everywhere I look, I see statements like "Scientists believe that the Earth formed 4.5 billion years ago," and it drives me up the wall. Scientists infer that the Earth formed 4.5 billion years ago, based on their reliance on data and logic. We have physical evidence (lead isotope ratios from three different radiogenic systems, measured in Earth rocks and in meteorites) that all suggest the solar system's solid-state clock started counting 4.5 billion years ago. Because we've never observed anything other than the steady, statistical decline of radioactive parent isotopes to produce daughter isotopes, we assume that the past worked in the same way as today (actualism/"uniformitarianism") and that these empirical measurements have meaning. We logically deduce that the Earth is the implied age, but we don't "believe" it.

Similarly, I get apoplectic when students ask me "Do you believe in global warming?" No, I don't believe it; I'm convinced of it on the basis of (a) physical evidence (data) and (b) logical inference from that data. To spell it out:

1. CO2 absorbs infrared radiation.
2. Infrared radiation is reflected upwards from the surface of the Earth.
3. CO2 is produced by the burning of coal, oil, natural gas, wood, ethanol, and biodiesel.
4. We burn a lot of these carbon-rich fuels by oxidizing them.
5. CO2 concentrations in the atmosphere are measurably increasing.
6. Oxygen concentrations in the atmosphere are measurably decreasing.
7. Globally, average temperatures are observed to be increasing.
8. Therefore, based on #1-7, the increase in CO2 concentrations in the atmosphere is causing the increase in temperature.

There's nothing there to believe in. It just is. Fact, fact, fact, fact, fact, fact, fact, and a logical inference that stems from those facts.

Ditto for the theory of evolution by natural selection. It's not something I believe in; it's something I'm convinced of because it's logically coherent and supported by reams of data gathered over 150 years of hypothesis-testing.

If there is one thing that scientists believe in, it's that the universe makes sense. Our starting assumption is that the physical world operates according to unchanging laws which may be deduced if we're clever enough. On the other hand, if the universe is mercurial in its physical laws, then science doesn't have a chance of figuring things out because the laws that apply on Tuesday will be different from the laws that apply on Wednesday. It should go without saying that, as far as we can tell, this is not the case. The universe does behave in a consistent and predictable manner, insofar as we can tell. Ergo, science is an appropriate way to go about elucidating its structure and properties. No belief necessary.

Which words bug you? Chime in.

Labels: geologists, science and society, teaching, words

Last week, I mentioned some cool conglomerates I saw when NOVA adjunct instructor Chris Khourey and I did some field scouting. The main purpose of that trip was not to focus on the Culpeper Basin's boundary conglomerates, however, but the "Great Valley" of Virginia's Valley and Ridge province. The "Great Valley" is usually called the Shenandoah Valley in Virginia, because the Shenandoah River flows north through it. (Topographically, it continues north into Maryland, but the Shenandoah River isn't found there.) Sitting in the middle of the valley is a mountain range, Massanutten Mountain. And in the middle of Massanutten, there is another valley, the Fort Valley. As you can see below, Massanutten is a fence-like ridge separating the higher Fort Valley from the lower Shenandoah Valley:

In fact, rumor has it that the name "Massanutten" is a native American term for "basket." This describes the overall shape of the mountain/valley quite well. It probably won't surprise you to learn that this valley-in-a-mountain-in-a-valley pattern is due to differential weathering of folded sedimentary layers. In fact, the entire Great Valley is one big downturned fold, a syncline. Actually, it's not a perfectly smooth fold -- there are some wrinkles and minor folds within the overall down-turned structure, so we call it a synclinorium. The oldest rocks are therefore at the eastern and western edges of the Great Valley, and the youngest rocks are at the center of the Massanutten Synclinorium, up in the Fort Valley. It turns out that some of these rock layers are easily eroded, and some are tough. Of particular note is the Massanutten Sandstone, a quartz-rich, well-indurated rock that is responsible for the ridges of Massanutten Mountain. It weathers away more slowly than the shales and carbonates (limestones) above and below it. Here's a cross-section view to show how the subterranean structure influences the surface topography:

The map view up above (using Google Maps' super-cool new terrain feature) and this cross-section also show the difference in landscape texture (and geologic cause) of the Blue Ridge province in the SE corner of the images.

In discussing the geology of the area, I'm going to mix my pictures from Thursday's scouting expedition with photos from Saturday's actual field trip with my Audubon class.

Let's start at the beginning. The first stop was in the Conococheague Formation, a late Cambrian limestone. Our field trip stopped at a nice exposure near Mulberry Run, west of Strasburg, VA. Here's the crew looking close at the outcrop, and trying out their geo-interpretive field skills for the first time:

Albert tests the outcrop with some dilute hydrochloric acid. It fizzes!

Soon, we spot the first of several stromatolites:

There are also some nice spherical grains of calcite called ooids (or ooliths). These form in wave-influenced carbonate banks today, like the Bahamas.

Interpretation of this environment then? Looks like a nice passive margin, far from any major terrigenous inputs (i.e. mud or sand). Warm tropical temperatures leading to the chemical precipitation of lime mud from seawater.

What comes next? On to stop #2, the Tumbling Run section* south of Strasburg, we see a nice long exposure of the New Market, Lincolnshire, and Edinburg Formations, a series of Ordovician limestones, all dipping nicely towards the axis of the synclinorium. (Last semester, one of my Honors students looked at silicified trilobites in the Edinburg Formation.) As you walk downhill (and up-section), you see a change in the limestones. They get darker in color, and they start splitting into thin sheets along clay-rich layers. Uh-oh, we're getting an increasing clastic influence on these sedimentary rocks. They no longer record pristine, Bahamas-type environments. Now the limestone is mixing with shale. Where is all that mud coming from? A hint may be found in several bentonite layers, weathered volcanic ash deposits. There's some volcanoes getting closer to the area, it looks like.

In the late Ordovician, the east coast of North America experienced the first of three episodes of Appalchian mountain-building. Geologists infer that the Taconian Orogeny was caused by the collision of a volcanic island arc (like modern day Indonesia) with the east coast. The Tumbling Run section shows well the increasing clastic influence of the growing Taconian Mountains to the east.

It's also good for some small but interesting tectonic structures. Check out this conjugate pair of en echelon tension gash arrays:

The black nodules you see along bedding in the above image are flint nodules, very characteristic of the Lincolnshire Formation. If you get close to them, you'll find that they exhibit different mechanical properties than the limestone that surrounds them. They are more likely to break (brittle behavior) than flow (ductile behavior):

But let's get back to the stratigraphy, shall we? (It just doesn't do to get distracted by these minor structures!) Our next stop was to look at the Oranda Formation (calcareous shale), indicating heavy clastic influence (but still a bit of carbonate). Then, after a lovely lunch at the Strasburg Emporium, we headed off to the Buzzard Rock Trail, to look at the Martinsburg Formation. The Martinsburg is a nice thick batch of fine sand and mud interpreted as turbidite deposits. Various pieces of the Bouma sequence can be seen throughout the formation, including graded beds, ripple marks, and cross-bedding. This picture conveys these alternating lithologies, representing fluctuating current strength as turbidity currents periodically brought coarser sediment into the deep (low-oxygen, as indicated by the dark color) basin.

Now, keep in mind that all these sedimentary layers later got folded during the final phase of Appalachian mountain-building, the Alleghenian ("Alleghany") Orogeny. At that same time of intense deformation, some of these mud layers began to convert to slate. The outcrop on the Buzzard Rock Trail shows this pretty well, in spite of being covered by lichen, algae, moss, and other horrible rock-obscuring growths:

The sandy layers outcrop as stiff, blocky strata. But look to the right of the quarter: in the muddy layers, a penetrative cleavage has developed, subperpendicular to the compressive stress. Here, let me draw for you what I saw at this outcrop:

The clay minerals in the mud are more susceptible to being alligned by tectonic forces than the grains of sand in the coarser layers. So the shaley intervals exhibit a more pronounced cleavage than do the sandy intervals.

But again, I'm getting distracted by the tectonic overprinting! This trip is supposed to be about stratigraphy, pure and simple. Doggone it! Okay, moral of the Martinsburg: no more carbonate by the late Ordovician. Instead, this sedimentary basin is getting filled with clastic debris shed off the Taconian Mountains** to the east.

Next layer up is the Massanutten Formation: mainly quartz sandstone, but also some quartz pebble conglomerate. We see it by entering the "basket" via a water gap near Waterlick, VA. Driving south (uphill) along Passage Creek, we were soon surrounded by looming cliffs of quartzite. It represents fluvial and beach facies as the depositional basin was filled to the brim. Here's a boulder of the conglomeratic portion:

Here's some nice cross-beds in the sandy portion exposed near Blue Hole, about 4 miles south of Waterlick, VA:

Other Massanutten Formation features include some fossils. Here's some poorly-preserved brachiopod external molds:

And here's some Arthophycus horizontal trace fossils, probably made by polycheate worms:

Okay, I can't resist this tectonic structure: an awesome anticline exposed along the Veatch Gap Trail (eastern part of the synclinorium, where a small anticline in the Massanutten Formation is superimposed on the larger synclinal pattern):

Beyond the Massanutten Formation, we are in the Fort Valley proper, inside the "canoe" shape of the Massanutten Mountain ridge system. Next layer up is some upper Silurian / lower Devonian carbonates, representing a return to passive margin sedimentation after the end of the Taconian Orogeny and the erosional beveling of those ancient mountains. Unfortunately, there are no good places to stop on the narrow Fort Valley Road, so I don't have a picture of them to share. Trust me, though: they're there.

The next good stops are of Devonian shales. There's some nice ones exposed across the road from Elizabeth Furnace. More mud? From whence does it come? We interpret this again as the onset of an orogeny, in this case the Devonian-aged Acadian Orogeny, which dumped a big thick wedge of sediment into the Appalachian Basin. Here's a shot of the Needmore Formation, one of these shales with distinctive trace fossils highlighted by iron oxide:

The overlying Mahantango Formation (Devonian) is a siltstone that bears a decent number of body fossils, like these brachiopods:

Here's something that may be the back of a trilobite (if I'm not imagining the lobe to the left of the central line of knobs), or maybe a crinoid (if the "central" line is all there is):

Here's what appears to be the (vertically-oriented) trace fossil Daedalus, which I learned for the first time this spring in Silurian rocks near Buffalo, New York:

Finally, at the top of the stack, near Seven Fountains, there are exposures of more bentonite, in this case the Tioga Bentontite, a major stratigraphic marker bed throughout the Appalachians. Here's a shot of the bentonite exposure on the Fort Valley Road near Seven Fountains:

Here's Chris looking at the outcrop:

To summarize the Fort Valley portion of the story: after the Taconian Orogeny ends, we get a brief period of tectonic calm and passive margin sedimentation (carbonate), and then a return to orogenically-induced clastic sedimentation (augmented with volcanic eruptions). In the sedimentary sequence of the Massanutten Synclinorium, this records the onset of the Acadian Orogeny. The actual deformation of all these sedimentary horizons into a synclinorium shape was accomplished by the Alleghenian Orogeny: the much bigger mountian-building episode triggered with Africa and North America collided in the latest Paleozoic.

Hope you enjoyed joining us on this trip. Virginia's got some great geology, eh?

* For the Tumbling Run section, I highly recommend this excellent field guide:

Fichter, Lynn S., and Diecchio, Richard J., 1986, "The Taconic sequence in the northern Shenandoah Valley, Virginia." In: Geological Society of American Centennial Field Guide - Southeastern Section, p.73-78.

** Note I don't say "Taconic." The Taconic Mountains are a modern topographic feature in New York. They exhibit Taconian rocks well, and the orogeny is named for them, but the Ordovician Taconian Mountains would have been much bigger and more areally extensive.

Labels: fossils, primary structures, sediment, stratigraphy, structure, teaching, valley and ridge

Periodically I post book reviews on this blog of geology-relevant books. I haven't done too many of these since I started the blog because it's been the spring semester, and that means I've been too busy to read. But now that the summer's here, I've got a bit more time. Today's tome is Last Child in the Woods, by Richard Louv.

The theme of the book is "nature deficit disorder," a condition the author loosely defines as adults not caring about the natural world because they never spent any time outside as children. Setting aside the quasi-disease-sounding name (which Louv acknowledges as being iffy), it's pretty much a priori that if you don't know something, you don't value it. When children spend their time playing video games instead of romping in nature, they end up caring about the one and not about the other. Last Child gets a little tedious making this point over and over: do you really need a whole book to explain that?

In the course of that protracted treatment, however, Louv brings up some good points. For instance, natural play has been effectively "criminalized" in our (U.S.) litigious society. We care so much for our kids' safety that we prevent them from doing anything dangerous. He also makes the point that nature education has dropped off, resulting in lower knowedge about natural systems.

Some passages rang particularly true for me. On page 139, Louv describes an observation by Robert Stebbins, an old-school naturalist (and professor emeritus at the Museum of Vertebrate Zoology at the University of California, Berkeley). Stebbins has been going out to the California desert for many years studying reptiles and other critters. The rise of ATV (all-terrain vehicle) recreation in his study sites has obliterated the local wildlife. He found that 90% of invertebrate life had been destroyed in popular ATV areas. I'll quote Louv quoting Stebbins here:

What upset him most was not the destruction that had already occurred, but the devastation yet to come and the waning sense of awe -- or simple respect -- toward nture that he sensed in each successive generation. "One time I was out watching the ATVs. I saw these two little boys trudging up a dune. I went running after them. I wanted to ask why they weren't riding machines -- maybe they were looking for something else out there. They said their trail bikes were broken. I asked if they knew what was out there in the desert, if they had seen any lizards. 'Yeah,' one of them said, 'But lizards just run away.' These kids were bored, uninterested. If only they knew."

Labels: books, environmental, teaching

Here's another transcript of one of my field trips, again from uber-dedicated student Jill.

--- T R A N S C R I P T --- B E G I N S ---

Prince William Forest Park - Field Notes
Hike April 6, 2008
Paper due: Sunday, April 20th

Transcription Note - I apologize for the lack of words, at times. We were so near the river, the background noise of the river made it difficult to transcribe. Also, it rained during the morning. It was not the best day for a hike, but the weather outsmarted all of us that weekend.

Valley - Quantico Creek - Main Creek
South Fork - Main Tributary

(Tape #2?)

Field Notes - Weather: Raining...Callan cautions us about being nice to one another in the rain...

On Trail Observation - Top of high hill - rounded river gravel mixed in with sand & clay

On top of another hill - we will talk about it.

Volcano erupting signage. - Hawaiian volcano example. What it would have looked like 500 million years ago. Chain of volcanic offshore islands spewing out lava. As time goes by subduction is bringing those to the edge of North America until they eventually collide. Then all igneous rock - basalt rock gets slathered onto the edge of North America. Ex. - A snowball. New basalt rock is packed onto the edges - younger material added onto the edges.

Continents (low in density 2.7) never subduct. Oceanic crust subducts (2.9 vs. 2.7). Whenever the two butt heads, oceanic crust loses. Result is isotopically dated rocks which make up the continents and ocean floor. Ages are wildly different - 4000 million years (rocks which make up the continents) vs. 200 million year old (ocean floor). There is a huge difference. Continents are 40 times as old as the oceans.

Oceanic crust is constantly getting destroyed vs. continental crust which is constantly getting preserved.

Oldest rock is in the Northwest Territory of Canada.

Old Rag mountain. Rock from Old Rag is 1 Billion years old. 1 Page handouts. 1st event - Grenville Orogeny intruded granites into the crust. Granites are a symptom of mountain belts/building. And the granites cooled and became Old Rag. The Iapetus Ocean Basin was opened up. Cracks opened up into that granite into which mafic igneous rock (basalt) squirted into those cracks. Hiking up Old Rag - narrow little slots - which are those cracks. Floor is made up of dark colored, fine grained rock whereas the sides are coarse grained, light colored granite.

All that transpired before the stuff we are talking about today.

Volcanic rock is underneath us. We eventually will see it. First we will see sediments that accumulated at the bottom of the Iapetus Ocean right next to the volcanoes. Then at lunch today we will see some of this volcanic rock, itself.

We will get to see the rocks that made up volcanic islands.

We are at the boundary of sediments and the island arc further east.

Stop - signage. Small lake, dammed valley Sign about the Fall Line. 2 Virginia physiographic provinces meet. Region of the 1) Piedmont 2) Coastal Plain (as day goes by)

Boundary is the Fall Line. Coastal Plain is made out of very loose sediments, not stuck together in to a rock; loose gravel, loose sand, loose mud. Therefore, it is very easy to erode away. It is easy for water to strip it away.

Whereas the Piedmont is made out of hard rocks. (Like the ones we are gong to spend most of the day looking at). As water is draining from the Appalachian Mountains in the Atlantic Ocean, it is easy to strip away coastal rock and hard to strip away the Piedmont Rock. And, as a consequence, the boundary between the two you tend to get rapids and waterfalls. Those rapids and waterfalls line up on a line from Southwest towards Northeast - we call that line the Fall Line.

Here is the fall zone. The image on the left is a Geologic Map. You can see the difference in colors along the water. Coastal Plain layers vs Piedmont Plain layers. The Coastal Plain is draped on top of the Piedmont like a blanket. (see diagram). The deepest, therefore the oldest part of the Coastal Plain is a series of rounded river gravel. OK? Ring any bells? That is what we are looking at back there...these gravels. So, that is actually part of the Coastal Plain draped on top of the Piedmont. Right here we only find it on tops of the highest hills, but as we head east, it is found at lower and lower elevations. So, what we are going to see as we get down at the bottom of the hill - we are going to see our first little waterfall. Where the water of the South Fork of Quantico Creek which is the creek that carves this valley here where that is falling over some of these hard, difficult to erode rocks. And, then as we get down into Dumfries this afternoon, we are going to move out on the Coastal Plain itself where it is going to be very flat and the rock layers are very easy to erode. It is going to look very different - and it is a major theme we are going to discuss more over the course of the day. Since the sign is here, I figure I had might as well say something about it.

Stop. Our first actual outcrop of rock. I wanted to give you guys a chance to check it out. Outcrops are where we actually get to see some of the Earth is rock formations at the surface - and - you would think they would be more common, but they really are not. One of the reasons for that is we are trying to do Geology in the East. Out West, there are no plants, so all the beautiful rocks are exposed with these ugly forests that cover up the beautiful rocks. So, you only get to see the rocks where the forests have been stripped away. Like here, where a stream has cut down to reveal the rocks or sometimes when we build a road underneath. So, on the East Coast we are largely limited to the rock exposures that are in creek bottoms or in road cuts. We are at the creek bottom of the South Fork Quantico Creek coming out of that little lake from the dam upstream there. I want you guys to take 2 minutes. What you are going to do is examine them. I want you to make observations about this. I do not expect you to come up with the whole geologic history...

Little patches on the surface. Those are not rocks. Those are a symbiotic relationship between a fungus and an alga, right here where it is wet. Go.

So, yes. Yes, what is causing that? Something? The water. When these outcrops are first revealed they have nice angular edges like over here next to David. As the river flows over them with time they get worn down so they get nice and smooth. We will see some really cool smoothing out features downstream like the one, Kathy, you were noticing on that sign. Yeah, we will see some of that later on. Uh, Tee, what did you notice? OK, little sharp edges...OK...breaking...everything is parallel. We see this parallelism in the rock and that extends out to the stream making these little ridges of rock that extend out to the stream... (We will get to that - hold that thought). First, I want to talk about this parallelism that we are looking at here. Jill, what are we looking at here? Foliation. Right. Folio comes from the Greek word for plant or leaf - leaves on trees...(two choppers overhead go by...)

Foliation - originally folios to describe leaves and then eventually used to describe paper or books (a foliated structure...pages in a book parallel to one another is what we are seeing here in the rock). Something layered. What is it that is layered in the rock? Sediments from the breaking down of those mountains? Let us back up. You are right, but I want to make it a little bit simpler. What are rocks made out of? Minerals, right. What we are seeing here is the minerals all lined up in a certain direction. What force could line those minerals up? Pressure from what? A tectonic collision. The North American Continent pushing in this direction and the volcanic islands pushing in this direction. Let us go back to this idea of these two plates colliding - one is a volcanic island arc and one is the North American continent squishing together - this stuff got caught between - a sick analogy...a cute, little fuzzy kitten chasing a butterfly out in the meadow. Then it runs out into traffic on Route 66 and a big Mack truck comes along from one direction and a cement mixer comes from another direction and they collide head on and the kitten gets caught I the middle. The kitten changes its shape as a result of that collision - the kitten starts off with little kitten bones and fur all oriented in different directions, and as the two trucks collide, the bones get aligned perpendicular to the two trucks' collision direction. This is the mangled corpse of these sediments of /in the Iapetus Ocean. They have been crushed. They start off in all types of different directions. I will use my hands to represent two different directions - and then they rotate to the only stable configuration possible. Picture a bunch of papers on your desk. Push your hands toward each other and the papers end up lining upright the closer you put your hands together. The minerals here are all upright - all standing up essentially vertical that is..............See how straight this thing is? (A rock used as an example).

Break...then...

...bubble. OK. Did you guys see that in the back? OK, say again, speak up... "...crack in the rock and water filled in it, warm water and it crystallized into quartz." Right, and how do you know it was deposited by water? What is the clue that is telling you that? Hydrothermally deposited quartz. This white color is due to little tiny bubbles of water in that quartz mineral crystal. That is a sure indicator that that was originally deposited in a crack. Now, however, it is only the little chunk, just like that; then there is another little chunk there and another one there and there and there... They are a little bit pink because they have been stained by rust. Notice how they all line up in the same direction, too. Like this thing here is 7 cm wide by 40 cm long. Compression coming in East to West making everything line up North to South. Now, let us talk about the original sediments that got crushed here. (The so-called kitten). There are three rocks here in my hand; three different sandstones. 1) White quartz sandstone, 2) pinkish arkose (potassium feldspar) 3) greywacke - gray - all made of sand. This one is exclusively quartz. This one is a mix of minerals and has lots of potassium feldspar. Greywacke is a mix of sand and mud. It is a dark, gray color (clay as well). If I asked you to pick one of these three as the original source of these rocks before they got squished, which would you pick? Greywacke. See the color? If I put these three down, the one that blends in the most is the gray one, right? Now there are some other things influencing the color here, but yeah, if you zoom in on these rocks you will notice little grains which were originally sand and mud in this ancient, dead ocean - The Iapetus Ocean. When the tectonic collision happened, a lot of the mud reacted, becoming mica. Mica is another mineral, and a defining characteristic of mica is sheets; flaky sheets lining up one way once again indicating again that squeezing direction.

Zeta (sp?) was asking about some fractures cutting across, like here. See the fractures? There are a bunch of brittle features cutting across this rock. These rocks were squished in a flowing way and then later they were broken by brittle fractures. So, these brittle fractures may be related to the uplift of these rocks, over time. I do not know, or cannot say specifically if it is related to some tectonic cause.

But we know (with certainty) that that happened after the rocks had cooled down again. During mountain building, these rocks were hot and flowing. After mountain building, they cooled down and that is when they broke. To get these rocks to flow, they would have had to have been heated up to 350 degrees Celsius or so. Maybe higher. We will see evidence down the way of partial melting of these rocks. Partial melting yields granite magma. So, that is another symptom of mountain building. So, you have to get the rock up to 450 degrees Fahrenheit (when wet) in order to get it to melt. Using the Principle of Uniformitarianism, you can say they once were molten based upon how we know such rocks form today.

Greywacke. David - greywacke is from Old German for grey rock.

Making the distinction between a sedimentary rock and metamorphosed sedimentary rock...layers of sediment. You do not end up finding these big, long flaky bands of quartz...presence of all this mica. We do not get big deposits out there in the actual world where mica accumulates in big layers. We get layers of mud. So, the mica itself is a metamorphic mineral. Also, we do not see any continuity. As we look along the way here, we do not see that we can detect one layer of coarse grains or one layer of sand, mud, or anything like that. Instead, we see a sort of smeared-out looking feature. These rocks appear smooshed. What would you add to that, David? (The mica here is the metamorphic mineral, not a sedimentary mineral...B word....boudinage...)

Boudinage. French for sausage. Describe a rock layer that has been broken into sausage like segments. Right here, look at this you guys. 1,2,3,4,5 sausage links. This quartz vein is broken (as a brittle phenomenon). Also, the flow was pinched out along the breaks. There are pinched out ends, like a string of sausages all in a row. This occurs at 10-15km depth from crust...right at the transition between brittle behavior in the upper crust where rocks break, and more flowing behavior in the lower crust. Brittle means breaking. Flowing is like silly putty or bread dough.

So, I wanted to elaborate on something. See picture...4 parts. Something we can deduce about these rocks. A preserved sedimentary structure called graded bedding: layers of rocks that are coarse at the bottom and fine at the top. No graded beds here today, but at the Billy Goat Trail, you will see graded beds. That tells you how these sediments initially accumulated. I am correlating these rocks here with the rocks at the Billy Goat Trail, based on similarities in their mineral content, and my knowledge of the area. I'm saying these rocks exhibit all characteristics of Billy Goat Trail rocks except we do not see any graded beds preserved here. In the Billy Goat Trail, there are a few lucky areas where we see graded bedding preserved. Why do I care about graded beds? Graded beds are deposited by currents flowing along at the bottom of the ocean. (Picture of turbidity currents). These currents are very dense, sediment rich flows, that go along the bottoms and they slow down. As they slow down, all the sediments caught up in the rolled up water settled out. The stuff that settles out first is the big stuff. The stuff that settles out last is the light weight, really fine-grained stuff. So, you end up getting these graded beds forming. Those formed down in a location like this, down in the deep sea in what we call an abyssal fan or a submarine fan, where sediments are coming off some land mass piling up in the deep sea making graded beds of greywacke. Again, greywacke means nothing more than a mix of sand and dark mud. So, that is what this used to be. Then it got crushed up. When did it get crushed up? When the Iapetus was closing, good. As the Iapetus was closing (let me pull out another graphic here) it was a scraping up all that sediment. OK, the subduction zone was going down the hatch, but the sediment on top of the oceanic crust was getting scraped off. It was building up into a big pile; a big, jumbled pile of sediment. That is analogous to a bulldozer moving over the ground scraping up a big pile of dirt in front of it, OK? Where the bulldozer is like the island arc, and then in front of the continents are the sediments it is scraping up. OK? So, that is what we are on here. Really, these rocks here are the big pile of muck that got scraped off the subducted plate and then later it got squeezed between the islands and North America. So, we call this big pile an accretionary wedge. Now, Dean, you were talking earlier about California and San Francisco. San Francisco is still on an accretionary wedge. The difference between Prince William Forest Park and San Francisco is, Prince William Forest Park then had that accretionary wedge caught between two continents; Africa and North America, and it squished. Whereas San Francisco, it just filled out. It has not been squished between two continents, yet. Give it another 50-70 million years, something like that. OK. Questions? (Why the silt...? C. - What silt are you observing? Does that just look like it is going into the hills?) What was stable in the middle of the mountain belt is no longer stable. The mica is rotting away. In fact that is why over here, when I was running my fingernail through these little grooves, there is a groove there to run my fingernail through. The mica is soft and it rots away really easily, so it ends up etching out. And, the quartz is very stable and so it does not erode away easily and that is why it makes these little ridges. So, guys if you have not felt this for yourself, come put your finger on the rock and feel this yourself. That is why, like, on the drive down I was noticing these big white boulders on the drive in. Those big, white boulders are made of quartz - it is stable. It does not break down over time. That is why when you go to the beach; the beach is made out of quartz sand. It is not made out of feldspar sand, mica sand or anything like that. It is quartz. Quartz is the stuff that lasts. (Student questions Callan. C. -- Yeah, right. Black beaches are where you are really very, very close to a basalt source. And, there are not...there is not ....adequate time to break down all those unstable minerals, so the beaches built up making those black minerals there. So, we are finding that there are some black minerals even on beaches here on the East Coast, but, the majority of it, when it is a nice mature beach, is quartz sand.)

One of the exercises I had Jill do this semester, and I had Dave do last semester, as well as the rest of my Physical Geology class is that I give them a little, bite-sized Snickers bar and they have to suck on this Snickers bar. The chocolate dissolves away very readily in their mouths followed by the caramel. The nougat lasts about 10 minutes or so. But even after you suck on this thing for about half an hour, the peanuts are still there. Peanuts do not dissolve, right. Peanuts are like quartz whereas all the other ingredients in the Snickers are more like other less stable minerals.

(Student talking about some observation). C.- Actually that is a great observation. Let us take that one step further. Imagine, now this creek here is not a creek but a road and you are driving down it. You take this turn and you take it a little too fast. Which way does your body get pulled? Right, towards the outside of the curve. So, basically, during flood times the creek comes in and slams into that wall right there and strips away the plants and strips away the leaves and strips away the dirt and it exposes rock there. Whereas the rock that is underneath the hill here is not getting hit head-on by the force of that creek. So, it fills up with sand, dirt, and leaves over time. I did hold this rock down here and I just wanted to point something out, it is a little bit difficult to see because the stupid thing is all wet, alright, just like us. But, this is a foliated metamorphic rock. Does everyone see the plane of foliation? So, if I were to line it up here with the regional foliation, it would look like that. Alright, but this one is loose so we can pick it up and examine the plane of foliation itself. And, there are little black needles there on the surface. Do you see those little needle-like minerals? They are needle-like mineral growths. Do you guys see them there? It is almost like if somebody took a bunch of chopsticks and dropped them on a desktop. The chopsticks were in this random orientation because they would be parallel to the surface of the desktop. OK? If I took all your pens and dropped them on top of someone's notebook, they would all splay out on top of that notebook but some might be pointing this way and some might be pointing that way. That is what you are seeing here in this plane of foliation. These are amphibole minerals. And the amphiboles are randomly oriented within the plane of foliation. Pass it around. I know David wants to get a good look at that with his lens. Make sure he gets that. Great. Good. (David and Callan have discussion about amphibole, spelling, etc...David asks, does the random orientation of the amphibole suggest that was it done when the pressure has been released. C. - No, I think basically that what we have here is we have flattening. Remember what we talked about was the different types of deformation; folding, faulting, and I think I said squeezing or flattening. These rocks have been flattened. And what we see is that the dominant pressure direction was coming this way and then the rocks, in order to accommodate that (here we go – here is my little Nerf ball. Yeah, I left my kitten at home...) Um, they are getting squished in this direction. Right now the Nerf ball ends up basically elongating outward this direction and growing in this direction, as well. So, like, you think about three dimensions, these right here are growing and this one...whhish....gets squashed. So, I think what is happening here is that flattening stress is causing the amphibole as they are growing...they ca not grow in this direction. It is like, try growing if the building collapsed on top of you. But, you can grow in this direction.)...we will see a couple of them here today. ...Dave, unfortunately it is not...it takes certain elements to make the amphibole, so unless those elements are present in the original sediments, you do not make it. Dave - OK. Student - Do you want to leave this here? C. Yeah, that is why I brought it down. C. - No, I would not break it, I would just kind of stash it over there underneath a tree or something so maybe in a year from now I can find it.

Another segment...

...you take away the fact that we have determined that these used to be sediments in the Iapetus Ocean basin, and then they got squeezed due to mountain building. Due to that Taconian Orogeny...this episode of mountain building that we mentioned back in the shelter. Taconian stands for the Taconic Mountains of New York, alright. (see the one page handout that I gave you). Dave - What are the compass directions here? C. - Essentially, North/South and then, East/West - squishing. Now is it actually that? Well, no its North/Northeast, but close enough. Dave - it is a good observation to make in the paper the direction in which the squishing seemed to happen. C. - Yeah, I would say that would be a great observation to make in the paper. Um - it may not have been originally in that direction though, because remember a later collision happened. That later collision also squished. So, it is like remember the kitten, Mac truck, cement mixer pile-up we had earlier? Then along comes a tank and crashes into it, OK? And then that ends up rearranging everything again. Dave - could the magnetic poles have changed here? C. - Uh, yeah, but we have no magnetic signature in these rocks. We are just trying to get in our head how - Dave - You did say North and South...C. - Yeah, so we are using modern day directions but then again North America would have been rotated around in a different position, so it is a complicated question. Sounds like it is a simple question but it is really not! Another student asks a question. C. - You do not have to understand about magnetic poles to understand what we are talking about...Dave - ...unless it is present day...(Callan brings discussion back around to)...yeah, that is all we have to work with and that is what is going to be most readily available to you guys. So, again, the one thing to think is this foliation essentially lines up on the same line from the Appalachians, basically from Georgia...Dave - OK, yeah, that is a better way to go, yeah. C. -....so, that, that is due to this first collision...Dave - ...Appalachians...to the ocean, like that? The Appalachians have...to the Ocean, like that? C. - Well, the Appalachians would be parallel to this. So, essentially we are looking at Maine up that way, Georgia down that way...ok, West Virginia, that way, and then the Atlantic out this way. Uh, I was in the middle of making a statement there and I got derailed.

(Dave - If these clay minerals had all been aligned and micas formed in the first compression, and they were tilted up in whatever orientation, and a second collision took place and it came from a different angle, would all this seem likely to get reoriented or would it preserve some of the old orientation? C. - Probably you would have some preservation and some would get reoriented, depending on where you have little bits that poked out, those being more susceptible to being re-rotated.) Um, that being said the overall structural grain of the Appalachians is this North/Northeast to South/Southwest direction, so, I mean I think we can just sort of simplify things - well, it may be an oversimplification - we can simplify things by saying these collisions all essentially came in one after another from the same direction. First, these volcanic islands during the Taconian Orogeny. There was a second collision that happened, later on, we are not really going to talk about that today - called the Acadian Orogeny. And then finally, Africa hit and that was the Alleghanian Orogeny. So, all these different orogenies were episodes of mountain building.

Oh, I know what it was that I was going to ask! When does the Taconian Orogeny happen? Well, Dana, that is just great. How did you know that!? She says 460 million years ago is when this actual collision took place. And, she is right, but, she is just pulling that number out of thin air. You can not see it. Student - she got it out of the papers C. - OK? Yeah, you are on the right track. OK, radioactive decay. So, certain minerals when they form, they take in radioactive isotopes, and then if you can go and you can say that that mineral is a mineral that only formed during an orogenies, then you can say, "Ah ha!" All you have to do is look at the radioactive isotopes that remain in that mineral and compare it to what they decay into. So, in this case the mica here has been isotopically dated. What they did was they looked at radioactive potassium 40 that is present in that mica and they compared it to the daughter product - the stable daughter which is called argon 40 And, the mica as we said earlier formed during metamorphism ...was a good state for the orogeny. The date is 460 million years ago. We are going to see a granite today, and the granite has a date of 464 million years ago. OK, so it is basically the same age. And it tells us about the same event, and granites, you remember, are another symptom of mountain building. So, we have got a really good view on the orogenies then by dating these two independent, isotopic systems. The metamorphic mica here, and then the granite that resulted from partial melting. I will remind you of that again when we get to the granite, OK? Alright, that is a good point to keep in mind. Student - So what overall type of rock is......C. - No, this is not granite, granite is much lighter color and granite does not have this foliation. Um - so this is a metagraywacke. All right. Meta, the prefix meaning change, and, greywacke telling you what it originally was.

OK., I know everybody is hungry, so we are going to hoof it. We are going to walk down to the Cabin Branch Pyrite Mine. We are going to be walking across and along the South Branch of...

...stop and maybe point out this point bar......do not feel like you have to take notes. OK, I’m not going to go over anything really important...


(Tape #3) After lunch...

OK, so granite you remember is produced by the partial melting of other rocks - remember I showed you that other diagram where you had a bunch of starting minerals and then the light colored ones sweated out - they melted? Whereas the dark colored ones stayed behind. So, here, it is a metagraywacke that is being partially melted. And the minerals that are easiest to melt those metagraywacke are quartz, feldspar, and mica - some of those are basically melting out and they are leaving behind the darker colored minerals. Ok, so we are producing these granite blobs and these blobs of magma are moving up to the crust and eventually they are settling down and crystallizing into granite. Remember we call these blobs plutons. So, here in this diagram which is part of your handout, I have got a diagram showing you some igneous plutons, OK? So that bodies that were magma and have crystallized into solid igneous rock, like a granite - OK, here is one pluton, here is another pluton - they cooled underground. Now, basically these plutons are these wet batches of magma and they are moving up through the crust. What happens to the pressure that is on them the higher up they go? Yeah, it is released and as a result they erupt - basically the granite separates out and the stuff that is most readily removed leaves the granite. So, think about a bottle of soda - did anyone bring a carbonated soda? David did. David brought a ginger ale. So, when he popped the top on that, OK, it started off as just liquid, but when he popped the top he released the pressure on the liquid inside. And as a consequence, a gas that was dissolved in the soda came bubbling out. Carbon dioxide came bubbling out of the solution. The same thing is happening to this granite which, remember, originally was magma. As it gets up to shallower depths in the crust, gases and things start coming out of it. It is leaking fluids into the surrounding rock. OK, so it is intruding into this rock and so these fluids and gases are penetrating the surrounding rock. Some of those fluids and gases would probably be water vapor, another one would be carbon dioxide, another one would be hydrogen sulfide, um a bunch of different fluids, OK? And one of the things that these fluids are taking - with - them, (I think I have got my mouth.../sandwich repeat) - OK, the fluids are carrying with them metals. Alright, metals readily dissolve in those fluids that are carried out of the granite by the fluids. And as those fluids penetrate the surrounding rock, they cool down and the metals are deposited there. Frequently, the metals are - they glom onto sulfur. Sulfur joins up with lots of different metals and then it settles out in this big sulfide deposit which surrounds the granite pluton. OK? So, it is kind of like a halo or an aura surrounding the pluton is this big aura of sulfides deposits - sulfur mixed with metals. OK? So, some sulfide minerals contain galena, some of you are familiar with galena, it is beautiful, it is got this silver luster, and these little cubes. Um, another really important one is pyrite. Pyrite is nothing more than iron sulfide. The chemical formula for iron is Fe - the chemical for pyrite is Fe. OK, it is nothing more than iron mixed up with 2 sulfurs. For every one atom of iron, there are two sulfurs bonded to it. And that makes this mineral called pyrite. Then, what color is pyrite? Golden. Yeah it is sort of this golden color and it looks a lot like gold, if you do not know what gold looks like. Um, it is got that same golden luster. Well, they were mining this pyrite here. We have already said it is not gold so why are they mining it? What on earth is the point of pulling up fool's gold from the ground? Gunpowder. C. - Gunpowder. So, basically, they are not interested in iron, they are interested in the sulfur. The main thing they are using the sulfur for is gunpowder. It is also used in many other industrial applications like making soap and refining glass and other things like that. But, not nearly as exciting as warfare. Jill - Civil War? C. - The pyrite mine right here actually started in the aftermath of the civil war, and then it actually hit a fever pitch during WWI, when there was a really big demand for gunpowder. So, they were pulling lots and lots of pyrite out of this mine, processing it to extract the sulfur and then using it to make gunpowder. So, geologically why there is a mine here is that the granite is essentially sweating out all these fluids. The fluids are rich in dissolved metals. It is just like when you sweat, there is salt in your sweat. And if it dries out on your shirt, you get a little white crust left behind on your shirt, right? So it is the same thing her except for instead of salt crustiness left behind, you will see a metal crust. So, the same granites that were produced during the Taconian Orogeny were sweating out these deposits of pyrite into the crust. Later on, people came along and said, "Hey, we can make use of that, let's make a mine here. We will dig into the hills and dig out as much pyrite as we can." So where we are right now is we are sort of geologically on this dome surrounding one of theses plutons, OK, we are in this sweaty armpit region. So, what I want to do now, is I want to go and find some pyrite and look at it. So, what we are going to do is walk back over here to this area where there was nothing growing. And, we are going to go look for some pyrite. Does that sound workable? Eventually we will come back to this place, so if there is something heavy you do not want to carry, you can leave it here and then come back and pick it up again. (Student question - inaudible. C. - The granite pluton was. Yeah, so the granite - the body of magma which would eventually cool into a granite. We will visit that granite this afternoon). (Student - So it is coming out because it...C. - the granite was, yeah, and as it is getting to shallower depths in the crust, it is devolatilizing, so the various gases that are dissolved in it are coming out. So, it is starting off here during partial melting, then the granite is organizing itself into these blobs, they rise through the crust, as it rises it is sweating out into the surrounding rock all these mineral deposits. Alright, sometimes as it moves into the crust, the crust cracks open and you end up getting veins of pyrite or veins of hydrothermal quartz. Some of those veins of hydrothermal quartz have gold in them, actual real gold. Including in the northwestern corner of this park, and by the Billy Goat Trail in the Great Falls area. So, there are gold bearing quartz veins in this area and they are coming from the same source. They are essentially being sweated out of this granitic magma. (Student - ...keep that in mind if the dollar keeps going down. C. - That is right, we will start mining our National Parks.) OK, other questions? Let's go.

(New Spot.) Now, I'm going to start talking now about some of the environmental damage that the mine caused. In this area, where the ground was near the mine operations, they were filtering the lower grade ore, you know the stuff that did not have enough pyrite in it, and they just kind of dumped it, alright? And, that is what we are sorting away here, right? And that pyrite is then soaking out here at the surface of the Earth in water, and that water is oxygenated water. And, those two ingredients end of completing a reaction of water, oxygen, and pyrite. Water, of course, is hydrogen and oxygen. Oxygen is just oxygen. And, pyrite is iron and sulfide. So, basically, after that reaction you end up getting iron mixed with oxygen and hydrogen which is rust (FeOOH) and sulfuric acid (H2So4). So, two things are being produced here due to the weathering of the pyrite; rust and sulfuric acid. Rust is what is making the soil so darn red right here. It is staining everything red. Look at David's boots right now - they are getting all soaked in this red mud. Alright, the other thing is sulfuric acid. What is the effect of sulfuric acid that you see right in this area? Basically, most plants cannot grow in super acidic soils; soils that are essentially drenched in sulfuric acid. As a consequence, nothing grew here for a really long period of time. It was basically a day of awakening - completely environmentally degraded. So, the ground was basically an empty wasteland and then the Parks said, "OK, we have got to clean up this mess." So, they took a series of steps to essentially reclaim the land. OK, this is something that frequently has to happen where they do mining - reclamation - basically making it look like a decent landscape again. And, what they did was they brought in a lot of limestone. Limestone is made out of calcite, and that reacts with acid. So, basically it is a buffer through the sulfuric acid. And, when they laid down all these limestones in the area, some of them are dissolving away as soon as they get set down. They are taking away some of that acid. It is kind of like Tums in the landscape - that is a great way to think about it? Did you have some Tums this morning? David - no. So, it is like Tums through the landscape and it is working better in some areas and not as well in other areas. It is not working so well right here. There is still a lot of sulfuric acid right here in this area which is why you can actually go and pick up rocks there. There are no plants growing out. That is thanks to the acid. Same as that little patch there at the end of the trail - there is nothing growing there. That is so weird for the East Coast to have an area where there are no plants growing. That tells you there is something seriously messed up with the soil underneath.

One of the things I would like you to do, is I would like to have you test the pH of the waterways. You might want to clean off your hands first, because the way you are going to be able to read this thing is to check the color of the paper. Alright, this is a little pH paper here. It is going to change different colors depending on the pH of the water you put it in. Now, you want to make sure you are putting it in relatively clean water otherwise you will get sediment on this which is going to give you a false reading. OK? So, I'm going to give everybody a little strip here. You can choose to test this water here, somebody should go test the water of the South Fork, and somebody should retain their strip so we can test the water of the Main Fork of Quantico Creek. OK, so we want to collect data at several different points, to several different iterations at each point, so we have reliance on the data and then we will share everything we get.

Everybody tests. OK, what do you have? 6! What do you got? (Everyone testing.)

Results 5 or 6 - somewhere between a 6 and a 5....slightly acidic. He just put it on his tongue and it is a 7. So, your tongue is pH neutral, which is a pretty good thing for your body. So, he has a reading of between 5-6 so that is just slightly below neutral, so this area is slightly acidic. That is not as acid as it once was, but it is more acid than just what regular old water would be which is 7. So, as the number gets lower in pH level, the more acidic. Higher is more alkaline. End of segment.

...sweating out of a granite pluton. Then the fact that this was mined for awhile for the purposes mainly of making gunpowder, and one of the elements that make up pyrite is sulfur, and then the breakdown of that sulfur at the conditions found at the surface of the Earth here; mixing it with water and oxygen, making rust and sulfuric acid, and then the Park surface had to treat the area by putting down essentially the geologic equivalent of Tums with limestone chips in order to get rid of the acidity. Oh, and another point that we could make here that the plants that actually are growing here are pine trees. These are acid tolerant plants. Their needles, themselves, are acidic. So, their needles are dropping - so look underneath those pine trees. You see the carpet of needles underneath, right? Those needles are essentially making that soil more acidic and that makes it harder for other plants to grow there, OK? They make a special kind of acid called a tannic acid. It is the same thing if you brew your tea for too long - it is a sort of bitter thing and it makes your stomach hurt. That is essentially what is going on over there with those trees. OK, let's move.

Testing pH at new location. (Dave - So are these the rocks that they dumped? C. - Yeah, so this is the ........that basically have water coming through them. The water is...)

OK, so I imagine we all do not want to stand here for too much longer. Did everyone see that vein of pyrite that Topher found? Time to work our way back to the path.

New location.

...C. - I'm going to turn upstream on Quantico Creek. (Jill - Confluence of Quantico Creek). We are going to look for a place to cross Quantico Creek. We want to be on the other side of it.

New location.

C. - I want to point out we are at the confluence here. So, here is the South Fork of Quantico Creek, which flows under the bridge we just walked over. Right, here coming into the main stream of Quantico Creek, the two merge right here (Jill - the confluence) and they flow downstream. Where we actually want to go is where there are a bunch of branches across the creek down there. It is probably only 200 yards from where we are right now. All right, but, unfortunately there is no great way to cross the creek right here. So, we have got to go upstream a ways, until we get to a good creek crossing. As far as a bridge and cross over. David, if you want you can wade across, but, I do not want to make every...

New location.

...flow. Where were these lava flows accumulating? Jill - Volcanoes. C. - Volcanoes, where were the volcanoes. Jill - the island arc. C. - Yeah, the chain of islands offshore, you remember, ancestral North America about 500 million years ago. Then, subduction narrowed the ocean basin between them, and eventually they got added on to the edge of North America. Now, how do I know these are lava flows? Great. Color, texture, and maybe the mineral content. Yeah, so there are some good color indicators here. What color is this greenstone? It is a very descriptive name - greenstone. It is probably in the Old German for - just kidding. So, greenstone is metamorphosed basalt. Remember basalt is what is coming out of the volcanoes today in Hawaii. (Student - asks question. C. - Well, we call it magma if it is below the surface and we call it lava if it is above the surface. Once the lava cools we have to give it a rock name. The typical name we use for the dark colored rock is basalt). Basalt is what made up the oceanic crust and what made up these volcanic islands. So, when the basalt gets metamorphosed it undergoes chemical reactions and those chemical reactions turn it green. The main green mineral here is called chlorite - it is basically a green mica. There is also epidote. Right here there is a pistachio colored mineral. You guys see that one? It is sort of a bright green? Filling in little veins over here? It is epidote. Alright, so basically, I know Topher is going to ask about this - the "take home message" is that these were once lava flows that got metamorphosed. How do we know that? The Principle of Uniformity. When you see lava flow that gets metamorphosed in the world today they change color into a green color. The reason is that they grow chlorite minerals and epidote. ....yeah, well there is some other stuff. Remember these have gotten squished. So, a lot of the original layering is lost. They are foliated. They are foliated and again it is that squishing effect. OK, I want you guys to come and look at these rocks here. There are little white circles in the rocks. Oh, see these white blobs here? OK, what is going on here is the same thing we were talking about earlier. When you release pressure on a lava, it causes gases to come out of solution. Just like when David opened his Canada Dry the bubbles formed. When lava erupts at the surface bubbles form in the lava and gases come out, right? If those bubbles do not pop before the lava sets up into rock they are preserved as little holes in the rock, like Swiss cheese. We call those vesicles. The vesicles have gotten filled in with mineral deposits. Those mineral deposits are known as amygdules. Amygdule is for the Latin for "almond." So, these were originally decided to look something like almonds - set in a piece of bread, like that. There are some really nice ones over here with mineral deposits. Generally the minerals that are filling them in are quartz, well Let us just say, quartz. David - something about popping. C. - ...if they do not pop, it leaves hole. Later on that hole could get filled in with a mineral deposit. This is important. The bubbles form as gases are coming out of lava, then some of those bubbles pop, we do not have any evidence of it. But, some of the bubbles do not pop and those bubbles get filled in later on with mineral deposits which make these little white blobs in the greenstone. And, notice that these little white blobs are not perfect spheres. Up here they appear kind of like this. Why is that? They got squished - like a little kitten's eyeball. That is due to that tectonic squishing. You can see that they are all basically squished like this line up at the plane of foliation. Alright, they lay exactly parallel to the plane of foliation. That is why the sphere became a pancake. So, they are little pancake shaped fossil gas bubbles from a lava flow. We call them amygdule because they got filled in with mineral deposits. If they were still empty holes, we would call them vesicles. ( ...you can see epidote down here in veins... come down here with David and you can see them.)

Barely audible due to noise from river. C - ...ancient volcano island rock... ...Chopawamsic....Dave and Callan in a lot of discussion about the volcanoes, flows, etc...evidence of it all...Callan sticks to history of Virginia....at one time you could have walked from Ohio to Morocco. Now those rocks were once sediments in the ocean deposited way down...

...discussion about potholes....barely audible. The role in carving it out. When water come flowing through here, there is a vortex of water. Filled with sand, silt, and it acts as liquid drill bits. Layers of quartz and mica, quartz and mica. Quartz stands out in high relief. Sand gets in there and preferentially eats away the mica. So, that is a pothole and potholes are one of the ways that streams are cutting down in areas of waterfall where they are adjusting from one level to another level. Alright, Let us go ahead and work our way back to the trail and we are going to start climbing uphill, towards the bathroom...

OK, so here we have another tree that is tipped over, and it has brought up a nice, fresh sample for us. We can see here more of that gravel that we saw when we first started on the trail today. This is not a rock. This has not been stuck together into a rock - it is just loose gravel...David - it is a root ball, right? C. - Yeah, it is a root ball of a tree. You can pick up the loose grains of sediment, and let it run through your fingers. Actually, I encourage everyone to do this. You will feel that this is a mix of sand and clay, and the clay will feel very sticky on your hand, and then these nice, rounded pebbles and cobbles of mainly quartz, OK? Most of which is present here is quartz. Student - Sand and all that is what is left over after the quartz was left. C. - Well, basically, you said it yourself. This is a very poorly sorted sand pile. This is a mix of different grain sizes, which indicates that it was dropped very rapidly. Now, what does the rounding tell you? Jill - it was well sorted. C. - ...well traveled. It is not well sorted, it is poorly sorted. Yeah, the rounding tells you that this quartz cobble started off somewhere far away and then it traveled a long distance to get here and as it traveled it got more and more rounded. This one must have started off a little bit closer. Alright, because this one is a little bit more angular. And that is typical of river systems because river systems end up draining a whole area. Rocks are dropping into them from far away and nearby and they are both tumbling downstream together. And, Jill, that is how you interpreted this, right? Jill - yeah, well no, sorry, I was off in a zone. C. - Jill, how would we interpret this deposit, how did this form? Jill - Well, basically, it came off of an uplift, and it traveled downward, and it was deposited into a system of water...C. - OK, what kind of water? Jill - Probably very fast. C. - OK, good, why do you say that? Jill - Because, it looks like they are rounded, I mean...obviously they passed through...Student - ...it is the size of the rock...C. Yeah, it is the size. Student - it is a well-rounded big rock. C. - Yeah, it is obviously a well-rounded, nice big cobble of quartz. And, it takes a lot of water energy to move something this size. Jill - Yeah, definitely. C. - OK, good, so what kind of body of water has the energy to move big cobbles like this? Jill - River, a river. C. - Yeah. Rivers, OK? Because we just saw, in fact, I just destroyed my vocal chords trying to shout over - rivers have a lot of energy. Whereas a lake does not have so much, a swamp - less. The ocean has a fair amount of energy, but you generally do not get big cobbles like this in an ocean because as soon as rivers flow into the ocean, they slow down, and then they drop all these things, and then they carry maybe the sand and the mud further out into the ocean. Those are all that really make it into the ocean. So, this is a river deposit. And, when you think about it you might think it is a little bit weird, because we were just down at the river and we just hiked uphill, and now at the top of the hill we see these river deposits? What is going on here, Cathy? Cathy - The river was once up here? C. The river was once up here, she says. These were not recent flood deposits. So, these are ancient, and the reason I know that is I can come up with a rough date for these deposits based on fossils that we find within this same gravelly unit. Now, this gravelly unit here, do you think it is a particularly good setting for preserving fossil remains? Callan hits the “unit” with large cobble, again and again. C. - Do you think that is good for a fossil? All right. Think about the river here. As these things are moving along, all these boulders are smacking into one another and grinding around. This is a lousy environment for preserving fossils. It is a miracle that we have any fossils at all from this unit. The fossils that we do have from this unit are very poor and they have been broken up a bit but we can still identify them and they are dinosaur bones. Alright, we found 3 or 4 different dinosaur bones from this one unit. There are some sauropod fossils, sauropods are the big, sort of lumbering, vegetarian dinosaurs with the long necks. We found some of their teeth and some of their leg bones. OK, there is a species called Astrodon johnstoni, it is the state fossil of Maryland. Basically, Astrodon means star-tooth. Think about your molars in the back, and you have these little points for grinding. There is a series of five radiating ridges for grinding up vegetation. So, Astrodon johnstoni. Also, we found some raptor fossils in here. At any rate, these dinosaur fossils date back to the Cretaceous. Cretaceous is a period of geologic time that ended at about 65 million years ago. It started at about 120 million years ago. The best estimate for an age on this unit is about 100 million years old. One hundred million years ago a river was flowing along this area, and that river was meandering. It was cutting in at a cut bank and it was depositing materials on a point bar. This is an old point bar deposit. OK, remember we saw piles of gravels that look a lot like this being deposited down at Quantico Creek today. So, this river was no longer cutting down, it was simply meandering back and forth on the landscape. Now, something must have happened between what we were just talking about at the base of the hill, and the deposition of these river gravels. We have this great big mountain range that had gotten built up, right? The size of the Himalayas - what happened to that? It was eroded down to essentially a flat level, and over that flat level, this river was meandering back and forth depositing gravel. OK? Then at some point after that what happened? Sea-level dropped and what did the river do in response? It started cutting down again and carving new valleys like the valley that we spent most of the day hiking through, OK? So we have evidence here of a higher sea-level at some point where these rivers were meandering along depositing gravels as they flowed eastward from the west out toward the young Atlantic Ocean. The Atlantic Ocean, by the way at this point, was 100 million years old. The Atlantic Ocean was born 200 million years ago and these gravels were deposited 100 million years ago, therefore, that is about 100 million years into the history of the Atlantic. One of the reasons that I’m able to say that these rivers were flowing from the west to the east, is we find signatures of rocks that we know only come from the west. Like we find pieces of granite that we find from the Blue Ridge Province. And these Blue Ridge granites have blue-quartz in them. Which is an indication that these are from the Blue Ridge Province. Yeah, there is some nice blue-quartz in this sample to right up there by my thumbnail. It has sort of a purplish sheen to it. You guys see that? The other thing that sometimes we find here is quartz cobbles that have a trace fossil right in them. That tells us that that came from the west, the river brought it this direction deposited it here, therefore that river was flowing from west to east. The same direction the rivers are flowing today. Now when the Appalachians were real, real young, it was the opposite. The rivers were starting here in the highlands above our heads and draining off to the west. Student - that is why you find Appalachian rocks way out in the west - west of us...C. - Yeah, there is some fairly compelling evidence in fact that the Petrified Forest of Arizona was buried underneath Appalachian sand and mud. In Arizona - so we are talking Mississippi sized rivers draining these young Appalachian Mountains, transporting the sediments to the west, and then basically they snuffed out a forest out there in Arizona. We can go and pick up a certain mineral from those sands, and that zircon has a chemical signature that is more analogous to the Appalachians than it is to any local source out there like in the Rockies. So, it indicates again at that time the mountains were here and the lowland was there. Who has got their handout handy, the one with the colored map on the back? Callan explains map....Kp designation which stands for Cretaceous. The sub p there indicates the Potomac and this is called the Potomac group. They are exposed up and down the length of the Potomac and you find them on tops of the highest hills. Same unit atop Tyson's Corner. You find it on top of Mt. St. Alban where the National Cathedral is. You find it on top of Mount Pleasant in D.C. - river gravels, river gravels, river gravels....Say that three times fast. So, this surface on top of which the river gravels are deposited is a period of missing time. The last geologic evidence we have in this area is the intrusion of granites. That happened around 460 million years ago, and then the next thing that is recorded in this area is the deposition of this gravel on top of it, which happened 100 million years ago. So, 360 million years of geologic time are missing in this area. We can say nothing about them from Prince William Forest Park. You have to read the geologic record to find out what is missing from those 360 million years. OK? Student - How come no one could think about water or erosion? C. To erode away a Himalayan sized mountain range takes a fair amount of time, and so it took a long time to grind down those mountains to that level. Plus, during the Cretaceous, the world was quite warm and sea-level was quite high. There was very little glacial ice, if any, and at that point then you have this combine effect of having ground down the mountains plus sea-level being high and that is when it deposited gravel all over this area. Wow, so this is like a little mud stone, right. Student - I get extra credit. C. - I would not call this a schist, it does not have nice physical minerals, but I would not mind calling it a mudstone. This is a little clast of mudstone and this is very typical of some mudrock layers that are typical out in the Valley and Ridge Province and that would be consistent with the story of basically transporting eastward. That is rose quartz there...OK, the first thing we are going to do when we get back to the visitors center is use the restroom, and then we are going to go and visit a fossil tree and that fossil tree is growing during the same period and it was probably growing along the banks of the river.

This was deposited by a river after the Appalachian Mountains were ground down. It is Cretaceous in age. It never experienced mountain building. If this had gotten caught up in that collision in would not be a loose pile of gravel, mud, and sand, it would be a rock. What would we call this if this had gotten cemented together into a rock? A conglomerate. Nature's version of cement with big chunks set in a little fine-grained matrix.

And, I do not really know what that means, I mean....

...on the trail today you are not leaving behind your skeleton, but you are leaving behind traces of yourself. Right? So, the thing that this Skolithos worm tube tells us is that it is a piece of the Antietam Formation. Antietam Formation is a big sandstone unit that is out on the western slopes of the Blue Ridge. And you can find them near Antietam National Battlefield, where the bloodiest battle of the Civil War was fought. You can also find this same rock along portions of Skyline Drive and there is an area where David and I have hiked near 66. There is a nice big exposure of it near Front Royal. So, basically it is telling us that the river transport direction was westerly - consistent with the blue-quartz. Sedimentary transport from west to east.

...Fossilized Bald Cypress Tree. It is really not in any danger of being degraded or anything like that, but it is in danger of having stuff grow on it. It is the mineral itself that will break down. All quartz. The quartz was derived from Cretaceous river gravels...And as it met this wood, it percolated through the wood, soaked into it, a chemical reaction took place, and it precipitated silica in place of the wood. This similar process has occurred in the Potomac Formation. In Washington DC, when they were digging out the foundation for the Ronald Reagan Building, they found more of these there. Also, at the base of the Mayflower Hotel, they found these fossil tree trunks down there. And, what do all these areas have in common? They basically have these cretaceous, Potomac Group river gravel deposits. So, you can imagine growing along the banks of this ancient river, Cypress Trees. How would you recognize a Cypress Tree if you saw one today? Yeah, Bald Cypress, and they have got these weird structures that rise up out of the waters. They call them knees - Cypress knees. They poke up above. I noticed in a place up here there are little tension gashes and they are filled in with silica, too. You see that - these little gray, blobs cutting across up there? So, it is like the tree itself is being deformed. It is fracturing and then the silica is depositing in those cracks. Yeah, so David is asking a question I do not have the answer to which is where is all this silica coming from in the groundwater? The groundwater has various things dissolved in it at various places at various sources, you know, that is about as specific as I can get. David - Silica does not dissolve easily in rainwater. C. - Right. David - It has to be warm to dissolve.

C. -...when things die, they just tend to rot. Fossilization is a very rare circumstance, when an organism gets preserved over time. Yeah, so wood tends to rot, so things eat it, beetles eat it. Well, one of the interesting things that is contrasted in this specimen as opposed to the one they found underneath the Reagan Building, or underneath the future site of the Reagan Building, is that one is jet black. This one is very, very light colored, it has got rusty. It basically suggests more oxidized conditions in terms of its preservation. Student - Where is the other one? C. - The other one is in Rock Creek Park. If you take my Bedrock of DC Geology Trip, then I will show it to you. It is jet black and it is also got pyrite preserved in it. Pyrite is again something that breaks down in the presence of oxygen as we have seen today at the Cabin Branch Pyrite mine...where it broke down into rust and sulfuric acid...so, it is more of a typical preservational environment. Low oxygen is more likely to be preserved. So, this is somewhat anomalous, but it is a beautiful specimen. What I just love about it is the grain of the wood here.

(Last segment - Granite outcrop in creek)

...water to get in there. What happens to water in the winter? It freezes. The water freezes and expands in volume by 9%. So, that opens up that crack a little bit wider. That means it is more than likely going to break down pieces, and when those pieces get broken out you carve out a little valley in the rock, right here. The quartz itself is stable, right? But, the neighboring area is not necessarily as stable. So, if you look around this area, you can actually see this quartz vein has actually become this little valley here and it narrows down...Do not take my word for it, come see. Now I want somebody who has never taken a class with me ever before, what is this? A sausage! What is the word for sausage? A boudinage! Oui! A boudinage! Alright, there is a beautiful boudinage in the last quartz vein, there. Now in order for boudinage to happen, it has got to be hot. It has got to be under lots of pressure, right? That is something that I said happened about 10-15km depth in the crust. So, that boudinage must have taken place during mountain building when this rock was still deep and hot, after the granite had already solidified because you ca not break a granite. It went through the quartz vein until the granite was already solid, right? So sometime after 460 million years ago, but before 100 million years ago. (Dave - Does the orientation of that, uh, boudinage tell you anything about the forces? C. - It well could. I have not measured its orientation myself, so I have not even thought about trying to put that into a regional context. But, yes, orientation of different rock structures like foliation or dikes, um - joints which are what we call these little cracks in the rock - those all often tell us something interesting about the forces that went to work on the rock. Now where Adrianna (student) is standing, we see a really interesting feature. Alright, here this granite dike has been faulted. You see here? This crack is not just a crack, it is a crack on which the two sides have moved relative to one another. There is an offset here about 1 inch in this granite dike. And, look here, there is another segment and it is offset about a centimeter. And, then another one, and another one, and another one, and another one. Do you guys see that? It has basically been broken and the rocks over there where Adrianna is standing have moved probably about, you know, just judging from this alone, maybe about by 5 inches that way relative to the rocks where I’m standing. That is a brittle behavior, OK? That is strictly breaking the rock. Alright, you do not see any real evidence of flow, there, OK, unlike the boudinage. (Background discussion/question...C - No, because this water does not have a lot of quartz in it. In order to get quartz to dissolve in water as Davis was pointing out earlier, it has generally got to be kind of warm to dissolve quartz better than cold water like this.) Student - What is the difference between a dike and a vein? C. A vein is just one mineral - like we saw epidote vein in the greenstone and we see quartz veins here. But, a dike is many minerals because it is an igneous rock. It is a tabular mass of igneous rock. And this is - this crack opened up, magma squirted into that crack, solidified into rock, and later it was broken and faulted. David - Wherever you see lines and stuff, you have faults. C. - We can only call it a fault if we have clear evidence of offset on either side. Still, like this one here maybe a fault as well, but I do not have anything good that tells me there is an offset on either side. Jill - So, instead of displacement in a rock, it is just a brittle behavior? C. - You might note that it is a brittle behavior that accommodates a displacement. The displacement can happen by flow or it can happen by breakage. In this case, it is breakage. Jill - It is a displacement? C. - Yeah, it is displaced. (...a 2 second bit of talking over each other/discussion back and forth between David and Callan.) C. - Cathy had a good question like did this happen during the collision? Alright, it is a great question. I would say that this is such a strictly brittle behavior (we can even see like little shards of the dike in there) right there along that zone, that I would say that this happened sometime after these rocks cooled down. And, earlier, I evoke this tremendous mass of rock overlying this location, right? 10-15 km of overlying rock that has been removed. Now, so does that mean that this rock, right here, has been exactly at this point three dimensionally in space through all of time and that there were mountains 15 kilometers tall on top us and have been beveled down to exactly this point? Or, did this rock start off 15 kilometers down and then basically uplift as erosion went to work on the landscape? Or, was it both? So, maybe it started off 7 kilometers down with 7 kilometer tall mountains. The mountains were eroded away, that means the crust is lighter and it pops up. Then more erosion goes to work on it. So, that means the crust is lighter and it pops up. More erosion goes to work - finally exposing the granite at the surface. David - are joints in granite often a loading and unloading feature anyway? C. - Well, a lot of joints in granite are unloading features. A joint is what you call a crack in the rock along which no movement has occurred. But, oftentimes we see that they are parallel to the topography. And these are distinctly not parallel to the topography. They are vertical. If we were to see a similar joint set running through the rock like this way, you know these rocks were under lots of pressure - now on the surface they are under no pressure. Sometimes we see granite actually expand, and then that thing fractures as it expands out, and those fractures then run like this, like an onion skin. That is stuff you see up in the high Sierras in California. Topher (sp?) was just saying he would been out there, up in Lake Tahoe - and then up in Yosemite to see these big granite domes, like Half-Dome, which are sheeting off layer after layer because the granite is actually unloading, and the sheets are just popping off. Are you making a movie of me? Jill - yeah. C. Just do not put it on You-tube or anything, OK? Alright, David noticed something cool, Let us turn our attention over this way.

Look at this. There are two intersecting joint sets here. Now, a joint set is basically more than one joint that is oriented the same way. So, we have got one joint that is basically going like this. OK, very regular. And, you have got another joint set that is going like this through the rock, also very regular. Their intersection produces these little columns like square columns of granite that go downwards, right. So, like we might actually see some up movement - no, none of them are loose. Well, anyhow, these things may be related to the unloading but if they were related to unloading, I would expect to see a third joint going like this through it basically divvying it up into tubes. We do not see that, but I expect it has something to do with tectonic readjustment during the uplift process. Alright, and after the rocks are cooling down and getting uplifted as the overlying rock gets stripped away by erosion, they crack, you know that is a stressful experience for a rock. It happens vertically, sometimes like 7 kilometers or 10 kilometers, something like that. Great observation. Now, what is colonizing those cracks there? Student -What? C. - Colonizing the cracks? Student - Lichen. C. Yes, and moss. Yeah, this is lichen. This is a crustose lichen, and this is a foliose lichen. Foliose lichen has leaves, right, like folios. And, the crustose is like crust on the surface of the rock. Um, yeah, because those cracks end up holding water, that is a good place for moss. Moss likes that - it grows along those cracks. You know, if I was to take a picture of just the moss here, to show you where the moss wants to cover up the joints...... (river is too loud).

How old is this granite? 464 million years old, + or - 5. That means somewhere in the range of 459-469 million years. OK, what else have you guys noticed? There are plenty of other cool things to talk about here? I'm going to climb back over there. C. - Good. I heard nickpoint, I heard waterfall, I heard pothole. OK, the river here is adjusting from a higher level towards a lower level. You can see that it is carving out a nice, deep valley downstream, whereas upstream we do not see that big of a valley. There is a valley, certainly, but its not a serious a size as it is downstream. There is a series of waterfalls downstream from here, and the river is adjusting to a ....level, over and over and over again. Somebody brought up the term nickpoint. I think you did. The profile of a river is like where it starts off at a higher elevation and then it is descending towards a lower elevation. Those little nickpoints are where the waterfalls are. Um, this is a nickpoint right here. This nickpoint is retreating in an upstream direction. Over time, the river will adjust, and basically will be cutting down in an upstream direction, and then the downstream area, if it gets too steep will try to get flat, by mass wasting which will widen the stream valley. Oftentimes we talk about the Grand Canyon haven been cut by the Colorado River. It is only partly true. The Grand Canyon was cut deeper by the Colorado River, and the Grand Canyon got wider over time due to a landslide, not wasting events. So, gravity does not like having a whole bunch of rock supported by neighboring rock. It is more likely to collapse. So, that is the same thing here. The Quantico creek cuts downward, and over time the valley has been widened and widened and widened. Sometime on your own come back to downtown Dumfries and see how wide the valley is, because it is quite wide. Alright, questions? Jill - Did you say earlier that was an example of columnar jointing? C. - No, I was just saying that the intersection of these two joints just end up making these kind of vertical four sided columns of granite. Like you take a block of cheese you go chop, chop, chop and chop, chop, chop. You end up having these little columns of cheese. It is not columnar jointing. It is a completely different process.

Where the moss was the first one to colonize this joint, so you can see that this joint is filled in with moss, and here there is frost wedging to get this expansion of the dike, and various other process have made a little deposit of dirt here in the crack. And, a seed landed in that dirt, and the seed took root. Is this an ideal place for a tree? Probably not. But, it is growing where it ended up. In time of really high floods, you know it is probably more than likely to be stripped away. Notice that the majority of the trunks coming off of this thing are all tilted in a downstream direction. OK, that probably happened during flooding. Um, yeah so, probably not ideal...

Jill - I have a question about nickpoints. Is it like the vertical cut in the waterfall? C. - A nickpoint is basically something we describe on a river profile. The way we recognize nickpoints is we look for water dropping from one level to another. Jill - it is not like an event...C. - it is a feature. Jill - ...it is a feature. C. - And, I would only be comfortable here saying this is one nickpoint here, and there is another waterfall downstream where you get another sort of 10 foot adjustment. I would say that is a second nickpoint. And, one of the neat things at Great Falls is that as you hike along the Billy Goat Trail is, when you go up to Great Falls you can clearly see one, two, three jumps in elevation. There are three nickpoints bunched together at Great Falls. Here, they are more spread out. Jill - but there was an event that created it, right? Callan - Basically, as sea-level drops a new water fall develops there and then that starts working its way upstream. So long as it outpaces sea-level rise it is going to keep propagating upstream. Dave - ...sea levels are rising. C. - Well yeah, I mean sea levels are rising, so lower nickpoints could get drowned and then there is not going to be any more erosion going on. Jill - so basically they are faults...they are faults? C. - No, a fault is a break in the rock in which movement has occurred. These are simply levels in the rock - the river has eroded down to this level, then as base level drops, OK, the river is now eroding down to this level. So, a waterfall develops here and then it moves upstream over time. But, the actual rock underneath is not necessarily faulting. Jill - OK.

Yeah, this is an interesting blob here. I'm noticing this shape. It juts inward here and it juts outward there. It appears to be faulted where this side has moved over to the right relative to that side. That side moved to the left. The way we typically describe these things is when you have a fault - say there is a fault running through here about like that, OK? You look across to the other side, and you use the direction that side tends to move. In this case, the other side looks like it went to the left. It's a left-lateral fault.

--- T R A N S C R I P T --- E N D S ---

As before, I would be pleased to hear any comments / insights / suggestions you might have.

Labels: field trips, nova, piedmont, teaching

One of my most dedicated students (a) recorded our field trip last week to the Billy Goat Trail, and (b) transcribed it. Because I'm pretty much overworked at this point, I haven't been very blogophilic over the past couple of days. My apologies. So I'm going to offer you Jill's transcription of the Billy Goat Trail geology field trip instead. I've made a few small edits to clarify, but otherwise it's her transcription of our discussion/my lecturing at the various stops. I find it an interesting document... who would have ever thought anyone would pay this much attention to what I have to say?

--- T R A N S C R I P T --- B E G I N S ---

Billy Goat Trail Field Notes - April 8, 2008

Canal - C and O Canal stands for Chesapeake and Ohio. It's the canal that was originally intended to link the Chesapeake Bay watershed with the Ohio River. The Ohio River drains into the Mississippi River. So it's going to basically provide a watery link across the Appalachians. This specific structure right here as part of the canal, is what? It's a lock. The reason they went through all the trouble of building the canal where there's a river right there is you can't sail a river up a waterfall. Right here, there's a major waterfall [Great Falls] that prohibits navigation upstream and downstream. They built this canal where boats could sail upstream in a series of steps. These boats were actually pulled upstream. Technically, they weren't sailing. They were pulled along by mules. The mules were attached to the boat by a rope. The mules would pull the boat through these narrow, little chambers. Then these gates would swing shut at the downstream end and they would open up these gates at the upstream end. And, water would fill it up until the lock was filled with water at the upstream level, there. And then the boat would be pulled on out and do the same thing making steps uphill. Only when you do something like that, allowing a boat to float to a higher level, can you actually move a boat in the uphill direction. And they would do the same thing going downhill. Again, you can''t sail a boat down the waterfall very easily either. It's a little bit easier than sailing it up, but it's still not very safe. So, the C and O Canal was built for that purpose. It was originally the brainchild of none other than George Washington who originally tried to build the canal to get around Great Falls on the other side - on the Virginia side; called the Patowmack Canal. It's a very small canal. You can see its remains today. But, this (the C and O Canal) was a more successful canal - ultimately it was not completely successful. Ground was broken on it by John Quincy Adams about 5 miles downstream from here. He took that first shovel, and couldn't get that shovel into the ground. He tried again and again and he broke a sweat - it was very embarrassing and then he was a very staid individual and he rolled up his sleeves and played the part of like... "I'm going to get this!"...and so eventually that's when the canal construction began. The canal never made it to the Ohio River. It made it as far west as Cumberland, Maryland. In fact, the canal is now over 184.5 miles long. It's almost 185 miles long; it's quite long. At some point, the Baltimore/Ohio Railroad was started. The Baltimore/Ohio Railroad ultimately proved to be a more efficient means of extracting the natural wealth from the Appalachians; timber, and etc... And, the C and O Canal fell into disuse and eventually it was abandoned. At some point, developers were talking about taking this area and turning it into a highway that ran East/West along the Potomac River. Then there was this Supreme Court Justice who stepped in and said, "That's a lousy idea. It's a beautiful area. We should preserve it as a National Park." That Supreme Court Justice's name was William O. Douglas. He challenged a bunch of senators and editors of various Washington newspapers to join him on a walk. They went up to Cumberland, Maryland and they walked down the length of the canal to Georgetown where it ends. At the end, all of them were convinced that this was a place worth saving. And so, it became a National Park thanks to that one man saying, "we need to preserve this place." The reason we're able to come here today and actually look at rocks and experience the landscape is thanks to those efforts made by him and others inspired by him. So, that's why this area is still in a reasonably natural state.

The Billy Goat Trail starts about a quarter mile downstream. We're going to walk the Towpath where the mules once towed the barges up and down the canal. Until we get to the start of the trail.

It's a bridge. However, that's a really big abutment for a teeny bridge like that. The only thing going over that bridge is people. Yet they've got these massive abutments that are 40-50 feet thick. (You can see this one goes off into the woods that way: the abutment). Why would they go through the trouble of making a massive, racking structure just for the sake of a little footbridge? Because of flooding - yeah. This is not a structure for a bridge. This has to do with flooding. Explain yourself. If you're a canal engineer, and you spend years of your life and blood, sweat, and tears making that canal, you don't want the canal destroyed by a flood, right?...shutting down commerce from east to west. You want some kind of a fail/safe that you can activate in times of flooding. That's what this is. This is a flood control structure. You can see that there are grooves there, and in those grooves are slotted wooden structures, kind of like this one that I'm standing on. They're thin at the edge, thick in the middle, and that allows them to resist water slamming into them. And, think about that for a second. If you just walk, ...walk past this amazing view over there to the right, and you saw the Potomac River down 45 feet below you, -- during times of flooding the Potomac River level is up here - during times of flooding the discharge increases and the depth increases, so that the river is actually where you're up here standing, now, during times of highest flooding. And that could be totally destructive to your canal. So, this thing is put here so that in times of flooding they could act quickly and move these things in and make a big wall there. The flood waters slam into that wall and they could divert it off into the woods here and dump back into the Potomac River's main gorge. That main gorge is what we're going to be hiking along today and as we begin walking along the Billy Goat Trail, which I see is officially closed... as we begin walking on the Billy Goat Trail, keep your eyes peeled for evidence of flooding. You're going to see some evidence almost immediately after we start down the trail. Some of you are going to recognize that evidence. Some of you are going to walk right by it and not notice it. Our goal today is to turn up our observation meter so we are observing more. So anybody once you see some evidence that indicates flooding, call it to my attention and we'll stop and we'll discuss. (Question, John.) OK, there is sort of a wetland area right here - a little sag area where the water table is intersecting the surface - we're going to talk about groundwater in lecture next week. Basically, the groundwater is right on the surface so you get standing water there - a small little wetland. Good observation but that doesn't indicate flooding. (Jill - how about all those trees and brush just kind of pushed to the side?) Good, all right, it's a good observation - it's got something to do with trees...

OK. I'm expecting you guys to pay attention today. Probably you're going to want to take notes because ultimately what I'm expecting you to produce for me as a result of this field trip is a summary paper. This paper is going to be about 3 pages long - something like that and the paper is going to describe the geology of the Billy Goat Trail based on what we observe today. So this paper is going to be broken down, essentially, into an observation and then a geologist's interpretation of that observation. And then another observation and how a geologist interprets that. And so by talking about the physical evidence, and then separating it from the story that geologists tell based on that physical evidence, you're going to get an overall history of what happened to these rocks over time. (The paper is due in two weeks).

Head of the Trail - walking from the beginning of BGT.

Right, so during flood times, the water is coming from upriver, it's slamming into that flood diversion structure, and it ...over the landscape in this direction. So you'll see that the trees here are preferentially tilted in that direction. Do you see this one? How it's tilted in that way? This one, in fact, used to have this as its main trunk. That main trunk was killed and a little branch became the new trunk. Or look at this one over here. See how this one is pushed out in the same direction? Both of the original trunks broke off. Here was one, here was the second. Then branches became the new main trunk of that tree. Do you guys see that? -- tilted in a downstream direction. And, if you look around, you'll see plenty... now just tilted trees doesn't necessarily imply flooding. Trees that are all tilted in a common direction imply that they were all knocked down by a similar force. Knocked down but not killed. See how many tilted trees you can count.

Not creep - creep is on a slope. This was not creep. Tilting trees.

Knocked down by a flood, then it continued growing. Those do happen to be knocked down in the same direction but I'm not sure they were knocked down by a flood. Basically because those weren't knocked down last time I was here, and we haven't had a flood since then. I'm extrapolating that they were not knocked down by a flood. Furthermore, there's still dirt in the root. If you had a flood up here that was strong enough to knock down a tree it would likely have stripped away all that dirt.

We do have a couple of people coming through. We do want to clear - just step aside and make a path - part the Red Sea here.

John has made an observation that there's a round boulder up there. And that round boulder looks really different than most of these angular boulders that we see up here. John, is it also the same sort of stuff - does it look the same in terms of its composition? No, so maybe that could have come from somewhere else and the rounding suggests what, Elizabeth? It traveled a long distance (very good, Sal), OK. Remember the farther a sedimentary grain travels the more rounded it gets. So, flood waters may have deposited that, or maybe the Potomac River used to be flowing up here at this level. We'll talk more about that possibility later on when we see more of these boulders. It's a little premature to get into that, but it's - uh - a pretty big boulder. It's the sort of thing that wouldn't be picked up by the current and carried in a suspended load. It's more likely to be bed load along the bottom. So that indicates that that may be evidence that this used to be the bottom of the Potomac River before it incised to a deeper level.

What I'm stopping here for is where we're starting to see some more rocks. We're getting down closer to the river and because this area is more frequently subjected to flooding, that means there's less vegetation here. There's less dirt here. And, we can see more rock here. Your assignment over the next two minutes is to figure out what kind of rock this is. I'll give you two minutes - you're welcome to roam all around this area. What you want to do is you want to find nice, clean surfaces and try and identify the minerals, the texture, and ultimately the kind of rock that this is. Keep in mind that there is junk growing on the rock surface like this. What is this thing? It's a lichen, right. Lichen is a mix of algae and fungus that grows on rock surfaces. So, don't look at the lichens; they will deceive you. There are many different colors; these grey blobs are lichens, there are black ones, there are orange ones. You want to look for nice clean rock surfaces that don't have any lichens growing on them. OK, two minutes!

OK, what I would recommend everybody do is find yourself a nice, hunky seat. We're going to be here about 10-15 minutes, discussing. Somebody start us off with an observation about some of the different minerals that you've seen, or some of the textures that you've seen. Quartz. Big blobs of quartz here (she's got acid she's been dropping and the rocks aren't fizzing - not calcite). Some of those are very striking and obvious - very creamy looking - big blobs like right here, right here on that knob, etc. Good. What other minerals do we see here? Mica - muscovite micas, the silvery micas. Sometimes it's really obvious like, look at this, look at the shine on that, great. Nice and shiny mica. What can you tell me about all those flakes of mica? Are they oriented in random directions? Or are they all aligned in a common direction (Jill - they're in sheets). They're in sheets, says Jill. Would you agree with that John? How about you Elizabeth? OK? Yes, all the micas are aligned in sheets. And, obviously some of these are boulders broken off. Some are bedrock where the sheets are still in their original position. Like the one Jorge is sitting on - this one here - the one Elizabeth is sitting on. What is the orientation of those sheets in space? If you took your hand and made your hand a flake of mica how would you orient it in space? OK, good. Doug is showing us with his hand the orientation of all those flakes of mica in space. So what is that? When you get these layers of quartz and mica all basically strung out in these vertically oriented sheets? It's metamorphic foliation. When we studied metamorphic rocks, there are foliated metamorphic rocks and non-foliated metamorphic rocks. These are foliated. What does it take to produce foliated metamorphic rocks? Pressure, very good, Vivian. What kind of pressure? (Confining pressure is what happens to you when you're at the bottom of a new swimming pool: it may cause your ears to pop, but it doesn't realign your head in a new direction). The answer is differential pressure. So, what's happening here is that these rocks have been compressed, OK? Force is pushing on them this way, and then another force is pushing on them this way. So, all those original minerals got squished together, and they ended up lining up straight up and down as they were squeezed from the sides. So, this is a metamorphic rock. You guys have just figured out something really important about these rocks. What tectonic event creates regional metamorphic rocks that have foliation? Orogeny. So, these rocks have experienced orogeny. They've been squished from the sides due to that tectonic collision. Whoa! That's a pretty big insight to come to about these rocks. I'm sure this raises all kinds of questions in your head. Go ahead and ask some of those questions.

(Vivian - no, talus is often great big blocks like this - talus usually accumulates at the base of a cliff. You might be able to call some of this talus - like this could be a block of talus. This is not - this is bedrock. It's still attached to the solid earth. It's not that it's broken off and made into a piece of sediment like this. You'll see some areas today where you'll see some large accumulations of boulder piles, and I guess you could call that talus. Remember talus is specifically when it's falling into place.)

Jill - we're in the Coastal Plain? No, we're in the Piedmont. Is this a part of the Taconian Orogeny? Well, one way we can answer that question - Jill's bringing up the Taconian Orogeny. I want you guys to think back to when we talked about the geologic history of Virginia in lecture. We talked about this mountain building event that happened in the early Paleozoic/late Ordovician Period, we call it the Taconian Orogeny because it built up the Taconic Mountains in New York - um - what caused that Taconian Orogeny? (Jill - we've discussed this two days ago - maybe I'll put you on hold there, maybe somebody else can remember what caused the Taconian Orogeny?) A volcanic chain of islands bumping into us? Exactly.

Awhile ago, there was an ocean off the East coast of the United States. If you were able to go back in time 500 million years, and hover over North America, you would have seen something that looked roughly like this. Here you've got a smaller North American continent and it's missing some pieces. Notice that Florida's not there, California's not there, Alaska's not there. OK, those have all been added on more recently. 500 million years ago California, Florida, and Alaska were not yet part of North America. And, our location is marked right here. Now actually at that time what we'd really see is this (see map rotated) - North America was in a different position at that time. And, since 500 million years ago North America has rotated and moved north. OK, but at that time it was on the equator and it was rotated in a different position. So today what we call the East coast was really the southwest coast. Let's just call it the East coast and keep it simple. Does that work for you guys? OK. Notice what's offshore there. There's a subduction zone marked on the oceanic crust by a deep trench, and then next to that, paralleling the trench, is a chain of volcanic islands; a volcanic island arc. Subduction is bringing that volcanic island arc closer and closer to North America. It collides with North America. Jill is fortunate because she took my Prince William Forest trip on Sunday. We actually got to go and visit some of the rocks from those islands. They're preserved down by Quantico, Virginia. In between those islands and North America, a bunch of sediments got squished out. I want to remind you guys about the concept of an accretionary wedge. Accretionary wedge. What is an accretionary wedge? Right. Sediments that get scraped off the ocean floor at the sight of a subduction zone. OK, so remember in class I offered you the analogy of my arm covered in peanut butter, and my other arm scraping that peanut butter that went there? There's another analogy at the bottom of a bulldozer. So there's this big pile of oceanic sediments building up at this trench at the sight of subduction. And, those sediments then begin to squash between the volcanic islands and North America. I gave you guys the awful kitten analogy, right? So, this is the crushed-up kitten. These are these poor little oceanic sediments that are getting squashed between a Mac truck, North America, and a mini-Cooper, these volcanic islands. So, the kitten's little bones started off in many different orientations when they rotate to newer orientation which defines the foliation of the kitten. So, that's what you're looking at here, guys. You're looking at rocks that used to be sediments on the floor of an ancient ocean, and got crushed up and metamorphosed into the rocks that you're standing on now. So, if they're now metamorphic rocks and they used to be sedimentary rocks, what kind of sedimentary rocks were they? (Basalt? No, basalt is not a sedimentary rock - basalt is an igneous rock.) Did anyone see any grains when they were looking at these rocks - any grain size? Grains? Check this out, OK? What does this look like? You can see sand grains in there. There are sand grains in here, and sand grains are made out of what mineral? Quartz. Good. What is reacting to make the mica? What is reacting under elevated conditions of heat and pressure to make mica? It used to be greywacke. Greywacke is a mixture of sand and mud. Yeah, mud is made out of clay minerals. These clay minerals are not stable at high temperatures and pressures. So when they experience it, they turn into mica. Muscovite mica that's all lined up in the same direction. So these rocks used to be layers of sand and mud at the bottom of this ancient ocean basin (so-it's metagreyacke - Laura). Right, good. So, for the rest of the day, I'm going to call them metagreywacke And, I'm going to use that term over a more traditional metamorphic rock name like schist because I feel like it tells us more. All that "schist" tells you is it's a metamorphic rock. The term metagreywacke tells us a metamorphic rock and it used to be greywacke. So, it's got a double meaning there. Now, what can you guys tell me about how greywacke accumulates or where it accumulates? (Jill - an accretionary wedge. C. - An accretionary wedge just takes whatever is there and jumbles it into a big pile). Greywacke accumulates from submarine fans at the bottom of the sea. What is bringing sediment down to that deep location? What depositional force? Turbidity flow. You guys remember turbidity currents? Turbidity currents are these big, sediment rich flows that flow down across the bottom of the sea floor. When they slow down, what gets dropped first? Big grains. What gets dropped next? The finer grain stuff. And you end up with this overall sedimentary structure known as graded bedding. Anybody notice any graded bedding here today? (Here's an example...)

OK, so there may have been some preserved but then the river eroded out those boulders and transported them away, that's one reason. But we saw lots of rock left. OK - maybe there wasn't that much there to begin with? That's a possibility. They changed too much - they've been metamorphosed? Yeah! Metamorphosis tends to destroy those original sedimentary features, right. I mean, even though the mud isn't mud anymore, it's now mica. Yeah, metamorphosis has destroyed most of the graded bedding. If you go up and down the Piedmont, back and forth across the Piedmont, it's very, very rare to find graded bedding still preserved in the metagreywacke of the Piedmont. The only place that I'm aware of that you can still see it - no I take that back - there are two places that I know of where you can still find it. One place is here, and the other place is out near Sugarloaf Mountain. But everywhere else it's been destroyed. Like, Jill, did we see any at Prince William Forest Park? (Jill - uh, no). No, right, it was basically too intensely metamorphosed and the graded bedding is gone.

OK, let's try and bring this around full circle now at this point. If these sediments were originally accumulating as graded beds of greywacke, mixed of sand and mud, in an ocean basin, what ocean was that? The Iapetus Ocean - what the heck is that? Before the Atlantic. How does it relate to its name? The father of Atlas... The Atlantic Ocean is named for Atlas - the guy who held the world on his back. The ocean that came in the same place as the Atlantic but earlier is named for the Titan who fathered Atlas, and that was Atlas's dad, and that was Iapetus. So we call this ancient ocean basin the Iapetus Ocean. The Iapetus Ocean no longer exists. It's dead. The Iapetus Ocean was killed in a series of tectonic collisions. First, was a collision between these aforementioned volcanic islands and North America. Second, there was a microcontinent out there in the Iapetus Ocean - that crashed into North America. That microcontinent is now preserved as most of New England. Right, you can go up there and visit that ancient microcontinent. And then, finally, a much bigger land mass crashed into North America, finally killing off the Iapetus Ocean. What land mass is that? Yeah, Africa. Are you feeding them answers over there, John? OK, Africa crashed into North America, and that made a certain supercontinent that I'm certain that everybody knows, without John giving them a hint, -- Pangea. The moment when the Iapetus Ocean died was the moment Pangea was born. As soon as those continents butted up against one another, the Iapetus Ocean was gone.

We're talking about a geologic history here... we're talking about a collision. Exactly, very good, you've got the journalistic instinct. Who, what, when, where, why, when...so when did this happen? How can we answer that question? (By isotopic dating...) C - of what? What isotopic minerals would you choose to date here? The muscovite. That's right. The muscovite is a metamorphic mineral formed during the orogeny. So if you get an isotopic date on that it tells you when the orogeny happened. Well it turns out people have done exactly that. They've taken this muscovite mica and they've analyzed it, looking at the isotopes potassium 40 and argon 40 in that mica. And that gives you a date of 460 million years ago. That's the date of the Taconian Orogeny, Jill.

OK, so the Taconian Orogeny just to sum up here. The Taconian Orogeny was an episode of mountain building that occurred 460 million years ago. (Radioactive parent isotope is potassium 40 and argon 40 is the stable daughter product - question...)

We already noted back there that the rocks had been metamorphosed. Remember that metamorphism is one of the characteristic signatures of mountain building. You can identify a mountain belt even when the mountains themselves have eroded away by the presence of metamorphic rocks.

There were two other characteristics of mountain belts that we discussed in class. Vivian - what's one of them? Folding. And that's exactly what Doug noticed over here. He noticed that the metamorphic foliation has been folded up here. You guys see those sweeping folds going through these quartz layers here? Right here, you can see another one here. Down up, up and down again. Along the trail today, you will see dozens upon dozens examples of layers of folding. Sometimes it's a little hard to spot with the lichens growing all over them. You can see some here - you can see the layers go up and down and then up again. There's plenty - you guys are going to see some real nice, sexy examples of folding as we go along the trail. This isn't the most amazing spot, but since Doug noticed it, I wanted to point it out.

While we're on the topic, what's the third characteristic of mountain belts? Metamorphic rocks, deformed rocks (including folded or faulted rocks), and then the third characteristic is...? Come on guys, you can't take this for granted! Granite! Right. Granite. Remember granites are produced by partial melting when rocks get really hot. So, you want to keep your eyes peeled for granites along the trail today, as well. OK. What we're going to do...

Find yourself a spot where you've got a good, unobstructed view across the river to the other side. Remember, we're in Maryland, and we're looking across the river at Virginia. So, Virginia' on the other side. There's a feature I want to call your attention to here. Can everyone see there's a series of vertical gashes? Four of these gashes all in a row? All oriented in the same direction? If you look for the tallest tree over there, and then go down to the base of that tallest tree you'll see these deep gashes in the cliff face. Those are a series of igneous dikes. Dikes are what happens when a rock cracks open, magma squirts into a crack, then the magma solidifies into an igneous rock. Tell me something about the igneous rock that is inside these dikes. Is it more stable or less stable than the metagreywacke? Less stable. How do you know that Michael? More mafic - how do you know that from here? The color? You can see it looks a little bit darker. It's a mafic igneous rock? Ding! You're right. I'll give you a closer look at it here in a few minutes. But you can also see that these igneous dikes don't project out from the face of the cliff, they're sunk into the face of the cliff. Which means, that that rock 'rots' away more easily - more easily weathered. It's more easily broken down. Remember the Snickers bar that I made you suck on? Whatever is making up those dikes is more like the chocolate and less like the peanuts. It's easily etched away. Everybody with me on this? So, that supports the idea of it being mafic because mafic igneous rock has lots of iron and magnesium. Iron and magnesium like to oxidize. Now tell me this. How old are those dikes? Younger than 460 million years old. How do you know that? They're cutting through the metagreywacke. And, you can't have the dikes cut across the metagreywacke unless the metagreywacke already exists. Therefore the dikes must be younger than 460 million years old. Well it turns out their igneous dikes, so what can you do to them? You can date them isotopically. They've done isotopic dating on biotite that's present in those dikes, and biotite gives a crystallization age of 360 million years ago. Only 100 million years after the greywacke got metamorphosed to metagreywacke. Again, that number is 360 million years. Those dikes are 360 million years old - 100 years younger than the metagreywacke they cut across.

I want to point out that the second Appalachian mountain building event occurred 360 million years ago. This is the collision of that microcontinent with North America. So, as we said earlier, North American experienced a collision first with a mini-Cooper sized land mass of volcanic islands. Now, it's colliding with a good-sized sedan - the microcontinent. Eventually, it's going to collide with a Greyhound bus which, would be Africa. North America gets to collide with larger and larger land masses through time. This series of dikes over here occurred at the same time at that second episode of mountain building, sometimes called the Acadian Orogeny. You can see it well up in Acadia National Park, in Maine. (The highest point on the East Coast, still, is Klingman's Dome in Great Smoky Mountain National Park; 2nd highest is Mount Washington up in New Hampshire) (John - Avalonia up North and Carolinia in the Smoky Mountains?) (C.- That could well be true but...) We tend to divvy up these parts of the Piedmont and call them different terranes - I know there's a terrane called Carolina/Carolinina... but, I don't know if that's necessarily a microcontinent. I would only call it a microcontinent if it's made distinctly out of continental crust before it hit. Avalonia is the name of the microcontinent.

Doug did a great job earlier with his hand showing me the orientation of the foliation of these rocks. Again, we can all see the orientation down at our feet right now. It's oriented something like this. Now what I want you to do with your hands is show me the orientation of these dikes. I specifically chose this spot to view the dikes because we are looking directly down the barrel of these dikes. We're looking down that crack in the earth - it's coming straight towards us here. If we're looking down at our feet, we should expect to see the dikes right here. Where are they? What gives? There's a shift. It turns out the dikes are on our side, they're about 30 feet downstream. Let's go see them.

All right, look at this. Here's some almost vertical gashes in the rock. They have that same orientation. But, if you look (and this is actually a great time to be running this field trip because there's not leaves on the trees yet) if you look over there on the opposite side you can watch these go down and you would expect them to run into the middle of that cliff over there. But, that's not where you see the dikes on that side. Instead they're offset in an upstream direction on the Virginia side by about 30 feet. You guys see that? Pretty cool! What gives? Maybe, a fault? Let's discuss the evidence for faulting here. Oh, by the way. Here's an example right here - this boulder that my foot is on here. That is the igneous rock that makes up the dike. It's a kind of basalt - you remember basalt from lab, right - mafic and fine grained? And, what you see here, and I want everyone to come take a look at this after I move away, is that this basalt has visible flakes of biotite mica in it. Not muscovite mica, that silvery mica that we saw at the first stop, but instead biotite mica, which is jet black. You'll see these little shiny flakes of black biotite mica here in this special basalt. This basalt has a special name. It’s called a lamprophyre, because of those flakes of biotite mica in it, but, it's just a fancy name for a particular kind of basalt. Alright, again that name is lamprophyre. You'll see that in your handout that I gave you earlier. So, these are lamprophyre dikes. How old are the lamprophyre dikes again? 360 million years ago, which is the same age as the Acadian Orogeny. (That's coming from you John- one thing at a time, one thing at a time...) So, Laura please share with everybody your hypothesis on why the dikes do not line up from Virginia to Maryland. All right. Because there was a fault, and that fault offset the dikes on opposite sides of the Potomac River. Here's two diagrams. If you can't see these, move closer. Basically, here I have two different explanations for the offset of the dikes on either side of the Potomac River. The first explanation is that the dikes were originally straight and they were broken by a fault. What kind of fault would this be? Left-lateral or right-lateral? Right? Yes. Right because if you're looking across it looks like the other side has shifted to the right. Very good. The other explanation is that in fact, the dikes were not straight dikes. There's no rule that says if you crack open metagreywacke it must be a straight crack. The crack may have been jagged. Maybe that explains the offset well. Unfortunately the critical area we need to examine to answer this question is underneath the Potomac River. So, if we're going to answer this question, we're going to need to look around for additional lines of evidence. One piece of evidence has to do with the shape of the river. This is an aerial photograph of the Potomac River. We started off our hike today up here at the Great Falls Visitor Center. This white line going across the Potomac River is a dam where they divert water for D.C. Great Falls itself is this great, white blob here. And, then, we are right about here following the Billy Goat Trail along a very, very, very straight section of the Potomac River called Mather Gorge. Mather Gorge is what we're going to be hiking along for the rest of the trip today. Mather Gorge is named for Steven P. Mather, the original superintendent of the National Park Service. You'll find that the National Park Service has honored this guy endlessly. I think I've slept in four Steven P. Mather Memorial Campgrounds in National Parks around the country. They really love this guy. Anyway, Mather Gorge is named for him. Now, look at how straight Mather Gorge is. It is incredibly straight: It's as straight as an arrow. It's as straight as you would expect if there was a fault underneath the river there that had ground up the rock. Remember faults tend to break up rock into fault breccia. And that would be really easy for a river eroding into the landscape to erode away fault breccia opposed to solid bedrock. So, the actual shape of the river is suggestive of the fact that there may be a fault underlying the river at that location. Unfortunately, the only thing that we can use as a marker is these dikes. So, we don't have any other evidence of offset here because basically everything else is just smooshed up metagreyewacke. And, the place is the end of Mather Gorge which is here and here, where you might expect to see the fault exposed up out of the river, you can't really see any good evidence of it. Some geologists claim they've seen it up on the Rocky Islands that we walked by just before the fault diversion structure. I've been there and I've looked at the same outcrop and I don't see indisputable evidence of faulting there. I see a crack, but a crack doesn't mean a fault. ("Can you put divers in the river?" Sure you could put divers there at great expense and risk to the diver. Problem is at the bottom of the river there's all kinds of boulders covering up the bottom. And, there's silt and mud and big catfish and you're not really going to be able to get a good look at what's going on. The one thing you could do is you could back up the Potomac River for a couple of days, excavate away, and arrive at an answer to this question, but its not really that critical a question to arrive at an answer at.) Let me share another piece of evidence for you. Remember there's another way of explaining the offset in the dikes. It may be a fault but it could also be that the dikes were not originally straight. Here are two pictures of outcrops of the dikes. One is on the Virginia side and the other is on the Maryland side. Let's discuss the Maryland side, first. This is a photograph taken from Virginia looking at Maryland. You can see coming up from the river, one, two, three dikes. And up here, one, two, three, four dikes. One, two three. One, two, three, four. Three does not equal four. What's going on? Well, it looks like this middle one is actually branching. It splits into two arms there. When the rock cracks it was a jagged crack and the crack had two little fractures – two little arms that went on and those filled with magma. The other photo is over on the Virginia side. Again you see the lamprophyre dike here the metagreywacke host rock here. And you can see another one of those branching arms coming off the dike. The dikes are not in fact straight. Does that mean that there is no fault? No. A fault could break crooked dikes just as well as a fault could break a straight dike. So, do we have an answer to the question? No. We do not know which of these two hypotheses is correct. We have not been able to prove either one of them false, therefore, they both stand as possible explanations for the offset of these lamprophyre dikes. What questions do you have? Jill - what questions should we have? How about: "Sir, can we look at the lamprophyre, please?" Jill - can, I? OK, yes you may! Come here, stick your head in that hole and check out the lamprophyre up close, and see how it looks different than the metagreywacke. It's dark, fine-grained igneous rock and it has little flakes of biotite in it. It's going to be difficult to see from far away, you actually have to get about a foot away to see that. C I'm not lying to you, you can trust me. So, don't take my word for anything. Trust your own eyes and your own mind.

OK, why have I brought you over to look at this rock? It's fancy. Take it further. Jill - it's been fractured. There's some fracture. What do you see, Vivian? There's a lot of different joints in these rocks - remember joints are fractures along which no movement has occurred. Those are visible all over here making this very blocky landscape. Look at the other side. You can really see the joints. Good observation. But it's not why I brought you here. There's a nice big blob of quartz there. What kind of quartz is that? There's a lot of different kinds of quartz that we saw in our minerals lab. Smoky, rose, citrine, milky quartz - milky quartz, good. Milky quartz is generally whitish. Why is it whitish? Yes, it's got little tiny bubbles of water in it. That indicates how that quartz got there. It got there by hydrothermal fluids. OK, basically hot water in the earth had quartz dissolved in it and it precipitated out these big blobs of quartz. Very cool, this probably happened during the Taconian Orogeny, as well, when these rocks where nice and hot. Again, not why I brought you here. There's a beautiful fold here in graded bedding. Alright, do you see that really coarse-grained layer there that's been folded up? That used to be horizontal on the floor of the Iapetus Ocean deposited by a turbidity current and then during mountain building it got squished up and folded. Squished up and folded and it looks like the hydrothermal quartz was then placed as well. You can see another bed here below it pulling the same trick. Pretty cool, huh? Symptoms of mountain building.

Jill asks questions about source of sediments. Thank-you for being persistent with that.

John, pass me some clam shells. Did you guys notice all these clam shells all over the place all over here in these big sand piles? All right? What's up with that? So you're saying that these clams are the same age as the rocks? Turns out that these rocks have no fossils, whatsoever. For several reasons. One is, deposits in the deep ocean, there's not a whole lot alive down there. Second, these rocks may be older than multi-cellular life. So, they may not have any fossils in them for that reason. Third, they were metamorphosed so any fossils present would have been destroyed like most of the graded bedding. So, these are actually Recent clams. It's actually an Asian species of clam that's an invasive species colonizing North American waterways. It's a freshwater clam. So, these clams have come downstream from higher in the Potomac which means that they were deposited during floods. Just like the tilted over trees are evidence of flooding, so too are all these clam shells and sand deposits way up here above the level of the river. Unlike that big round boulder we saw earlier, this is the stuff that usually gets picked up by flood waters. This is like a little parachute very easily picked up by the waters and wafted around. Good. Let's go.

When does the Billy Goat Trail actually going to get tough? It's about to get Billy-Goaty. So what we're going to do is walk across an area called pothole alley. And as you walk across pothole alley you'll see why it got its name. And there's going to be lots of potholes there, you've got to be really careful. You want to use your hands and your feet. It's a good time to be putting away anything you've got in your hands and you've got your hands free to navigate the landscape. Jill - are you going to stop and talk a lot? C. - No I'm not going to talk at all. We're going to walk across it and then we're going to get to the other side and sit down on a nice broad plateau and have lunch overlooking Mather Gorge. OK?

(right after lunch) Maybe sand, maybe silt. Um, one of the things that you learn about these potholes is that if you take your hand and you reach inside and you run your finger around the inside you'll feel differences - that there are little ridges in there. There are different layers of quartz and mica. Quartz stays up in high relief because quartz is very resistant to erosion: it's hard. Mica on the other hand is soft and chemically unstable - it breaks down into clay at Earth's surface temperatures. So, what this is telling us is that something is preferentially etching away at the mica and leaving the quartz behind. Something really small has to get in there to do that job. Something like a grain of sand or like a grain of silt. So, pebbles may be part of the process, but, definitely sand or silt are part of the process. They're etching away at the mica and then maybe a pebble comes along and slams into these unsupported ridges of quartz and snaps them off. That would be one hypothesis, but the original etching is done by sand and silt. Based on these little ridges.

There's something else you may have noticed, and that is if you look across at the Virginia side, there's this very flat surface, basically parallel with the surface that we're on. Do you see that? Because if you look back up river, there's this sort of flat plateau, maybe not really flat, - it's etched into with all these potholes and stuff, but it basically continues across the Virginia side. That is one of those bedrock terraces ("straths"). They're older levels of the river that used to be the river bottom and then the river cut into a newer, deeper level. Some of the evidence that we have for this being the bottom of the river are these giant potholes. This sort of thing is not going to be scoured out in a flood. It's something where you've got the river working on it for centuries - maybe millennia. ...potholes... also, there are these great big boulders that we find up here. Boulders that were probably once bedload at the bottom of the Potomac River tumbling along, rolling downstream and then eventually when the Potomac cut into a deeper level, they were left high and dry up here on the surface. The next thing that we're going to stop and look at along the trail is one of those boulders that tells us about where the river was flowing from. On the other side (of the river) you see a hill. There is a hill on the other side that rises above this bedrock of terrace steps. That hill is called Glade Hill. On the top of Glade Hill you also find rounded boulders that have been transported downstream by the Potomac River. So the top of Glade Hill used to be the bottom of the Potomac River. So, the bottom of the Potomac River was above our heads and where we're standing now was still solid rock. Then the Potomac cut down to a deeper level. It carved out this bedrock terrace, made these potholes, deposited the boulders here, then it dropped again and cut down to a deeper level. The Potomac is incising over time. (This is not an entrenched meander because the Potomace does not meander here. There are areas where the Potomac does meander, like at the Paw Paw Bands. But, here of course the river is quite straight.)

OK, I want everyone to come and take a look at something. Wow. Alright. What I want you guys to do is I want you to stick your head in the cave. Tell me what you see! Stick your head in there and look at the ceiling. What are you seeing? Folds! You're seeing folds and what's being folded? Alternating layers of quartz and mica. The quartz is light colored milky quartz the mica is dark-colored biotite mixed in with muscovite. And as you look up there you can see that they're strung out in parallel layers. Light minerals - dark minerals. Light minerals, dark minerals, light minerals, dark minerals. It's a very coarse texture. We learned a name for that metamorphic texture - you got coarse alternating bands of light and dark minerals –gneiss. Gneissic banding. So, you got this foliation and remember that the foliating is formed due to differential pressure during mountain building. But what happens to the foliation, here, Laura? The foliation was folded. So you see that these alternating layers of quartz and mica that have been all folded up. And, that's an interesting thing because when you think about it, those layers themselves formed due to pressure in one direction. In order to get them to fold, you have to apply pressure from another direction. This is important stuff here. This tells us that these rocks have experienced more than one generation of deformation. They've been squeezed once. They got to sit still awhile, and they got squeezed again. OK? Questions on this outcrop?

OK., we're going to go down the path. We're not going to go far because we're going to see a stange, green boulder in the middle of the trail.

A Martian! This is an interesting rock, this is a greenstone, clever name. And, a greenstone is metamorphosed basalt. Where does basalt come from? Mafic lava. It's what basically happens when a volcano erupts mafic magma we call that basalt. If you want to see basalt forming today go to the Big Island of Hawaii or Iceland. If that basalt gets caught up in an orogeny, it gets metamorphosed and it becomes a greenstone. Basically, two metamorphic minerals grow - both of them colored green. And you met both of these metamorphic green minerals during our metamorphic rocks lab. Olivine is not metamorphic-that's igneous. I introduced you guys to 5 metamorphic minerals in that lab - garnet, kyanite, staurolite, and then these two. Chlorite - deep forest green, and pistachio colored green - epidote. Epidote indicates hot water in metamorphism. So what happened is this basalt flow got metamorphosed and it produced this greenstone. Now that brings us to the question of what are these little white blobs that are popping through here in different places? They are little round or ellipsoidal blobs of quartz.

Think of what this lava would be doing when it was first erupting. "Kitty eyes." Ignore her! Aren't they crystallizing. Sure, they're crystallizing and they're fine grained texture which makes them a basalt. What does a basalt do when it gets up to the surface and suddenly it's depressurized? Air bubbles... Remember lava often degasses at the surface causing little bubbles that we call vesicles and then those vesicles, those little swiss cheese like holes in the rock they can later get filled in with mineral deposits. In this case, quartz rich ground water flowing through this deposited quartz filling in these vesicles preserving the vesicles as... amydgules. Amydgules are these preserved gas bubbles. Now, I'm going into a lot of detail about this one boulder, even though this boulder is not from this area. This is like I mentioned, a visitor. It is one of these boulders that was deposited on the bottom of the Potomac River, before the Potomac River cut down to a deeper level. This is a piece of a very distinctive greenstone that is present out in the Blue Ridge Province. It's called the Catoctin Formation. I mentioned the Catoctin Formation when we talked about our Geologic history of Virginia, when I said that when Rodinia broke apart there were these big lava flows all over the landscape - flood basalts; that's the Catoctin Formation. Later on of course those flood basalts got metamorphosed during Appalachian Mountain building which made it green. Jill - so these are actually far deeper - have been layered deeper into the landscape, right? C. And the mountain building they got shoved up and erosion exposed them to the surface. The reason I go into all this detail about the identity of this boulder is I know where this boulder came from. I know that outcrops of amygular greenstone - the Blue Ridge province is west of here. So that indicates that when the Potomac River was flowing at this level, it was carrying sediments from the west to the east. Now that may seem obvious to you because of the Potomac today - it flows from west to east. But, we can say with some certainty based on the presence of this boulder right here that that boulder was doing the same thing in the past (Principle of Uniformity). It's a confirmation that the flow direction of the Potomac has been relatively constant at least since it was at this level. OK, I'm going to show you some other evidence if that. I'm going to point out some other boulders along the trail as we go along and they’re all going to have Blue Ridge identities. But, first I've got something even more spectacular to show you.

So I stopped here to show you this outcrop which might not look something too spectacular in the beginning, but once you understand what this thing is your eyes are going to pop out of your head and your jaw's going to drop. Get in close, take a look at this. What do we have here? "Rocks." (Eyes rolling) Sure... there's some nice folding. There's some potassium feldspar in there. See these peachy little potassium feldspars, here? They're opaque relative to the grey quartz here, no longer milky quartz, but grayish. Potassium feldspar, grey quartz - what is that? What are we looking at here? What are these little blobs of a mixture of coarse grained quartz and potassium feldspar? Granite! What's the third characteristic of mountain belts? Granite! You're looking at metagreywacke that's gotten heated up so much that part of the metagreywacke has melted. Not all of it, but some of it. Remember the idea of partial melting where you start off with a rock with a bunch of different minerals. Then if you heat it up, some of those minerals basically dissolve into liquid magma and some of them stay as a solid residue. So, ones that are more likely to melt are the felsic ones. Those that are less likely to melt are the mafic ones. So, essentially what you're seeing here is granite magma being sweated out from super-hot metagreywacke. This rock was originally deposited as sediment at the bottom of the Iapetus Ocean. Then it became metamorphosed and now part of it is becoming igneous. It's all three parts of the rock cycle right here in one outcrop. Jill - it's coming back to itself. C. - right, its coming back to itself. Right now its being weathered off and producing new sediments, so the cycle runs full circle, right? This is a granite being born. You've just got these little blobs of granite magma leaking out of this rock. You've got the midwife's perspective here watching this granite in the act of being born. This granite magma is liquid it's going to go upward in the crust like the blobs in a lava lamp and eventually it will join with other blobs and its going to cool together into a big granite pluton somewhere else. But, here it never made it that far. It just started to sweat out of the rock and then it stopped. So we are lucky enough here to have this snapshot moment of the rock cycle caught in the act: caught red-handed where metasedimentary rock is actually converted into igneous rock. It would have had to be really hot for this to happen. Probably around 400 degrees or 450 degrees; something like that. But because it's coarse grained it cooled slowly underground. Now it's up at the surface today, but originally it cooled down slowly deep underground. We some evidence in this area where we see boudinage. Little sausage shapes squeezed out. Remember we see that at about 10-15 kilometers depth. So this is a rock that formed about 15 kilometers beneath the surface when it was about 450 degrees. Now are there 15 kilometers or rock above us now? No, they've been removed. What removed them? Erosion, yeah. Erosion ground down these ancestral mountains and exposed their roots. The rocks that we're looking at here were once at the roots of the Appalachian Mountains. (Laura - So this surface here could be an unconformity surface?) If something else were deposited on top of it - right here we don't have anything else deposited on top of it - we see these occasional little boulders on top and if you go look on the top of Glade Hill there's a nice layer of boulders over there.) Let these people through and we'll continue our discussion.

Migmatite - partially molten - Jill. Um - migmatite. What can we do with igneous rocks, like we did with the lamprophyre? Isotopic dating. So we can isotopically date this granite. It turns out this granite gives us an age of 460 million years ago. Same age as the metamorphism – same orogeny. The Taconian Orogeny heated up these rocks and squeezed them. What was the cause of the Taconian Orogeny? The collision of a volcanic island arc with North America. So, good work guys! Isn't this a spectacular rock?!!

I have traipsed across this old planet a fair amount and I've seen migmatites in only two places. I've seen them up in Maine, and I've seen them here. So, you're really lucky that you're taking a Geology class where you're really close to a place where you can go and see a migmatite. Most students are not that lucky. OK!

He's showing us the difference between fresh and weathered metagreywacke - Jill - he's showing us... we just looked at the migmatite.

By the way the smell you smell right here is sulfur. This is a creek here that evidently ...some sort of pyrite deposit. There's iron in the creek which is rust - iron oxide. And, it smells sulfurous. Remember that pyrite is iron and sulfur. Here, it's being broken down here by the water.

Is that why they have the ridges here in general? - student. Ridges - Jill Ridges of quartz extruding out of mica. - example/observation

Remember I showed you that image of the scuba diver and he's standing in the river and the sea level is rising over him. OK, this is the river gravel that was deposited in that river. It's part of the Weverton Formation - it's early Cambrian. It's about 540 million years old or so. And again, I wouldn't expect you to know that by just looking at it. I only know that because I walk around thinking about geology a fair amount and I recognize it here. So, I'm correlating this boulder with outcrops to the west. There's some other boulders here as well. As well as this reddish stuff. There's these reddish sandstones. We're going to talk more about those just over the hill here. Here is a nice example of diabase which is going to be related to this red sandstone. This is a mafic igneous rock because I don't want to give away what I'm about to reveal down the trail. But, there is a variety of boulders here. All of these boulders can be sourced to outcrops in the west. Again, more evidence that the Potomac River is being pulled from the west to the east over time, carrying sediments along to prove it. OK? Like little passport stamps telling you where it's been. OK, a little bit further and we've got two more boulders to look at.

Three different sandstones. I've got samples from all three of them here. Somebody tell me the name of one of these sandstones. Quartz sandstone - the white one, almost pure quartz. The other is greywacke - dark grey - that's what the local bedrock was originally. This rock (sample) is a greywacke, not a metagreywacke - these (bedrock) are metagreywackes. The pinkish one is arkose. It's a mixture of sand, mud, and potassium feldspar. Big angular pieces of potassium feldspar. The kind we saw in that granite. In terms of maturity, the arkose and the greywacke are immature sandstones, and the quartz is mature sandstone. We've already learned that the greywacke is deposited in deep sea fans, sometimes called abyssal fans or submarine fans. Where is quartz sandstone deposited? Beaches, good. And where is arkose deposited? Very immature, it still has all its feldspars it hasn't broken down to clays which means it hasn't come very far. Rift valleys. Arkose is a characteristic of rift valleys.

We have two boulders here which can help complete our sandstone triumvirate. We've already got the greywacke down - check that off the list. This one here is a metamorphosed quartz sandstone, so its made out of quartzite. It's a really interesting one. Do you see those little circles on top of it? Those are the tops of fossilized worm burrows. These fossil worm burrows project down into the rock like this. They're cylindrical; called Skolithos. Some of you have noticed Skolithos trace fossils in lab. I've got a few samples out on the countertop. They look like little soda straws running through the rock. Again, I know where that came from. It's from the Antietam Formation. That's a barrier island beach sand that's found in the – the river has traveled from the west to the east - all the others boulders I've stopped to talk about have been located in the Blue Ridge. This is also a Blue Ridge rock. The Antietam National Battlefield is what its named for - the Antietam Formation. Characterized by these little fossil worm tubes.

This red beauty right here, and I encourage you to do so, - these little pink specks are potassium feldspar. This is an arkose. A big beautiful arkose from 10 miles away. This naturally outcrops 10 miles from here. 10 miles upstream at a place called Seneca Creek. Because it outcrops at Seneca Creek we call this the Seneca Sandstone. Seneca sandstone is an arkose. So, Michael found a piece of this early on. We've been walking over various boulders of it all along. Its source is so close by we actually have a lot of it here. What else have we seen that's red sandstone today? The first stop we made - along the canal. The locks were made out of this red Seneca sandstone. It turns out to be a great building stone. This Seneca sandstone is quite young. Because its young, its actually younger than Appalachian Mountain building. Which means it hasn't been metamorphosed. So, it's essentially, it's wet, poorly-lithified sand. So that means that when you cut it out into blocks, it cuts like butter. But, then once you take it out, it dries out, and once it dries out it becomes much harder. That's the ideal building stone. Easy to extract from the ground but hard once you make something out of it. The Smithsonian castle is made out of red, Seneca Sandstone. The "brown"stones in Dupont circle, too...

This is a very interesting chapter in Geologic History because, as Laura pointed out, arkoses get deposited in rift valleys. We've talked about putting Pangea together, killing the Iapetus Ocean through continental collisions, but we all know that Pangea didn't last. Pangea broke apart, and when it broke apart, what opened up? Rift valleys. Some of those rift valleys filled in with sediment and they didn't keep opening. Some of the rift valleys connected together and became a new ocean basin called the Atlantic Ocean. This is from the site of a failed rift. The rift began to open, but it didn't keep opening. It is located to the west of here, called the Culpeper Basin. The Culpeper Basin is a Triassic aged rift valley. When Pangea was breaking apart this big gaping hole opened up in the crust filling in with immature sediments like this arkose and then it stopped. That's where you find Dulles Airport today - it's in the middle of the Culpeper Basin. But, some other rift valleys, over in that direction (east) connected together and they were the weakest link. That's where the crust kept ripping over there. And it ripped and it opened wider, and wider, and wider and eventually sea water came in and it became a little ocean basin and then it widened and widened and widened and its still widening today. And, that's the Atlantic Ocean. So, basically that process began around 200 million years ago in the Triassic, and this is a Triassic sandstone. What organisms were alive during the Triassic? Dinosaurs.

--- T R A N S C R I P T --- E N D S ---

If you've made it to the end of this post, congratulations! I'm sorry, but I won't be able to refund the hour you just spent reading it... But since you're here, I'm interested in your feedback about this -- what elements you read about here caught your attention? Why? Thanks...

Labels: field trips, nova, piedmont, teaching

NOVA recently updated their webpage, and now we have a big banner photo which changes every time you hit "refresh." A colleague pointed out that there's an image up there of the Snowball Earth field trip