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: 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, 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

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:

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.

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