Stonefly

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 throw a frisbee, and listening to bluegrass music, and eating.

The only photos I took were of this lovely stonefly adult (Plecoptera) that landed on my car.

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A lovely beast, yes?

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Macro Damselfly

I realize the geological blogging has been rather light around these parts lately – just one more day of “fluff” posts… Here’s a damselfly, photographed close-up last Thursday along Route 340 south of Elkton, Virginia.

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There were also some rocks there… more on them tomorrow.

3 bugs + 1 lizard

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 few good birds (eastern towhee male + female, some warblers), and some good wildlife, by which I mean more insects and reptiles.

Here’s a young bug (literally, from the order Hemiptera). Sorry for the lack of scale; this guy is like 2-3 mm long:bug_1

Fat, juicy caterpillar:bug_2

Beetle of some sort, with a lovely golden iridescence: bug_3

And a lizard:liz_1

Enjoy. Happy May!

Macrobeetle

A macro shot of a beetle (length ~11 mm) I saw on the wildlife-rich George Mason University structure trip two weekends ago…

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Neat iridescence, eh? I love macro photography, especially of bugs.

Eastern Worm Snake

While on our structural geology field trip this week, my GMU students and I encountered an eastern worm snake, Carphophis amoenus amoenus. The little charmer at first reminded me of a boa, like the ‘rubber boa’ I once found in California (a real animal, not made of rubber), and then I convinced myself it was a glass lizard… But upon the return to civilization, I was able to consult several webpages and confirm that it was in fact an eastern worm snake. Check it out:

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A distinctive “thorn” at the tip of the tail:

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Very squirmy and constrictional little fellow: nosing into me and poking me with his tail “stinger” repeatedly.

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Overall, a cool critter!

…We were also visited by swallowtail butterflies of several flavors:

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Quartz veins on Pimmit Run

Last Sunday, I took a solo hike along Pimmit Run in Virginia, accessing the valley via Fort Marcy, a Civil War fortification off of the George Washington Memorial Parkway. As always, I did a bit of geologizing along the route. One theme that emerged from the day’s photos was quartz veins. These veins form when the host rock (in this case, the Sykesville Formation) cracked open in a brittle fashion, then silicon- and oxygen-bearing hydrothermal fluids flowed into that fracture. As the fluids cooled, the silicon and oxygen bonded together and precipitated quartz, sealing shut the fracture like a seam of glue.

Here’s one that I liked because it outcropped both above and below stream level:

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In several places along Pimmit Run, I saw small zones of saprolitic bedrock, which is basically “rotten rock,” where the Sykesville Formation outcrops have been more pervasively chemically weathered. This one was so soft that I was able to dramatically plunge the blade of my Swiss Army knife into the rotted rock adjacent to an unweathered quartz vein:

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Oblique view of the same outcrop:

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As a structural geologist, quartz veins are interesting because they are extensional features whose orientation relates to the stress field these rocks experienced in the distant past. Once formed, however, they can also act as strain markers to show how subsequent deformations have affected these rocks. Here, for instance, is a folded quartz vein:

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…and here’s a bonus tiger beetle:
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