virginia

Falls of the James III: river work

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In today’s post, I’ll finish up with my geologic discussion of the falls of the James River in Richmond Virginia, south of Belle Isle. Previously, we’ve examined the bedrock at this location (the Petersburg Granite) and a series of fractures – some faults and some extensional joints – that deform that granite. Now we come … Read more

Falls of the James I: pluton emplacement

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Last Friday, NOVA colleague Victor Zabielski and I traveled down to Richmond, Virginia, to meet up with Chuck Bailey of the College of William & Mary, and do a little field work on the rocks exposed by the James River. Our destination was Belle Isle, a whaleback-shaped island where granite has been quarried for dimension … Read more

"Geology of Skyline Drive" w/JMU

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I mentioned going out in the field last Thursday with Liz Johnson‘s “Geology of Skyline Drive” lab course at James Madison University. We started the trip south of Elkton, Virginia, at an exposure where Liz had the students collect hand samples and sketch their key features. Here’s one that I picked up: Regular readers will … Read more

Stonefly

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This weekend I went camping with my family in Virginia’s Shenandoah Valley, near Berryville. I poked around with river cobbles and experienced fluvial dynamics firsthand with an inner tube ride down the Shenandoah River, but mainly I turned off the geology part of my brain. Instead, the brain enjoyed idling, and thinking about how to … Read more

Gorgeous poison ivy

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Spent the day in the field yesterday with Liz Johnson of James Madison University and her fun group of students in a “Geology of Skyline Drive” summer course. More on the geology later… For now, I just wanted to toss a group of photos of poison ivy up here. Look at this beautiful plant! Look, … Read more

"Those aren't pillows!"

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In the 1987 comedy Planes, Trains, and Automobiles, John Candy and Steve Martin have a funny experience. It involves a cozy hotel room (one bed only) and the two travelers are huddled up for warmth. As he wakes up, John Candy thinks he is warming his hand “between two pillows.” At hearing this, Steve Martin’s … Read more

3 bugs + 1 lizard

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Yesterday, Lily and I embraced my first day of no-more-classes by taking a hike. We drove out to Massanutten Mountain and hiked up to Signal Knob, a ten-mile (roundtrip) jaunt with about 1500 feet of elevation gain. Along the way, we saw a lot of Massanutten Formation quartz sandstone (Silurian), a few trace fossils, a … Read more

3,2,1, Contact!

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On my structure field trip just over a week ago, we found the contact between the Mesoproterozoic-aged Blue Ridge basement complex and the overlying Neoproterozoic Catoctin flood basalts (now metamorphosed to greenstone). This nonconformity can be found just west of the Appalachian Trail at the Little Stony Man parking area in Shenandoah National Park. Here’s … Read more

Ball & pillow in cleaved Swift Run Formation?

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On my structural geology field trip this past weekend, I made one major modification compared to last year’s iteration. I added a fifth detailed “field study area” at an outcrop of the Swift Run Formation, a Neoproterozoic sedimentary unit that is discontinuous in extent between the underlying Blue Ridge basement complex and overlying Catoctin Formation … Read more

Mud

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A few more photos from Pimmit Run … of mud. This mud has lots of interesting features, including dessication cracks showing lovely 120° triple junctions connecting up with their neighbors, raindrop impressions, and animal tracks. Tracks of at least three species here: (Clicking on this one will make it bigger) Mud: not as fascinating as … Read more

Transect debrief 8: late brittle deformation

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The final chapter in our Transect saga is now here. In some ways, it’s the least thrilling of the bunch. On the other hand, when I see a nice example of this structure, it makes me squeal like a little girl. I refer, of course, to plumose structure, the small-scale architecture of a joint surface. … Read more

Transect debrief 7: Brittle-ductile deformation

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On the transect trip, I also saw some nice meso-scale “minor” structures that probably formed during Alleghanian deformation. Prominent among the ones that really impressed me were these en echelon tension gash arrays, deforming the Antietam Formation quartz sandstone and well exposed in blocks used to construct the wall along Skyline Drive and the Sandy … Read more

Transect debrief 6: folding and faulting

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Okay; we are nearing the end of our Transect saga. During the late Paleozoic, mountain building began anew, and deformed all the rocks we’ve mentioned so far. This final phase of Appalachian mountain-building is the Alleghanian Orogeny. It was caused by the collision of ancestral North America with the leading edge of Gondwana. At the … Read more

Transect debrief 5: sedimentation continues

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We just looked at the Chilhowee Group, a package of sediments that records the transition for the North American mid-Atlantic from Iapetan rifting through to passive margin sedimentation associated with the Sauk Sea transgression. Well, if we journey a bit further west, we see the sedimentary stack isn’t done telling its story. The saga continues … Read more

Transect debrief 4: transgression, passive margin

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…So where were we? Ahh, yes: an orogeny, and then some rifting. What happened next to Virginia and West Virginia? Let’s consult the column… After the rifting event opened up the Iapetus Ocean, seafloor spreading took place and tacked fresh oceanic crust onto the margin of the ancestral North American continent. As North America (“Laurentia”) … Read more