Callan Bentley

Weathering on Old Rag Mountain 2: Opferkessel

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Yesterday, I pointed out an example of differential weathering on Old Rag Mountain, in Shenandoah National Park, in Virginia. Today, I’d like to shine the spotlight on another example of weathering to be seen along the trail there: little weathering pits that occur on the top of the granite outcrops. These are opferkessel. Some people … Read more

Weathering on Old Rag Mountain 1: feeder dikes

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Old Rag Mountain is a distinctive mountain in the eastern Blue Ridge of Virginia, contained in a little lobe of Shenandoah National Park. It’s a great hike on several levels: (1) it’s got no trees on the summit, so you can actually get a decent view from on top, (2) it’s got a great section … Read more

Friday fold: tortured turbidites at Devil’s Slide

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Marek Cichanski (of De Anza College near the south end of San Francisco Bay) contributed this week’s Friday fold: Marek says: The locality is a place near San Francisco called Devils Slide. It is a piece of the coastal highway built along a steep mountainside above the ocean. This unstable stretch of road was recently … Read more

Diabase intrusion at the Vulcan Manassas quarry

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When I was flying back from Phase I of “Border to Beltway” in Texas this past March, I was delighted to photograph a bunch of local geology from the air, including this prominent diabase quarry in Manassas: I had never been to this particular quarry before, but as it turned out, it was one of … Read more

Friday fold: differential weathering of carbonate intraclasts in mudstone

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Howard Allen is the documentarian of this week’s fold: Howard writes that this is: Middle Cambrian Chancellor Formation rock with recessive weathering intraclasts(?). Hamilton Lake trail, Yoho National Park, British Columbia. My interpretation of this one is a little shaky–it was raining when I took the photo (in 1982) and I was hiking with a … Read more

Palimpsest tales from a Silurian limestone

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My favorite rocks are those that tell multiple stories – rocks that are “palimpsest” with subsequent “chapters” of their biography capable of being teased out, based on different features to be observed in the rock. Click to enlarge What can we see in this small sample of the Silurian-aged Tonoloway limestone, from Corridor H, West … Read more

Faults in the Tonoloway Formation, Corridor H

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Here’s something fun: Click to enlarge Those strata are Silurian-aged Tonoloway Formation carbonates. There are plenty of dessication cracks to be seen, as well as salt casts, among the layers exposed. But more eye-catching at this distance is the faulting that disrupts the high-contrast layers… Both (apparent) normal and reverse faults can be seen in … Read more

The Moral Landscape, by Sam Harris

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Sam Harris wrote a couple of excellent missives on the downsides of modern religious thinking and religious institutions in The End of Faith and the sequel which rebutted some of the U.S. criticism from it, called Letter to a Christian Nation. He published a new major work in 2010, The Moral Landscape: How Science Can … Read more

A new diamictite exposure (Devonian?) along Corridor H

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While on Corridor H last week with Team “Border to Beltway” (and USGS research geologist Dan Doctor), we stopped at the putative mass transport deposit. We still haven’t figured out which unit this is (It’s not the Foreknobs), but as we approached it, Dan wondered aloud, “I wonder where the top of the Devonian is. … Read more

B2B Coastal Plain trip

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Last week, the “Border to Beltway” field exchange team went to Dora Kelly Park in Alexandria, Virginia. There, a ravine reveals the boundary between the Coastal Plain and the underlying metamorphic rocks of the Piedmont… My NOVA colleague Ken Rasmussen joined us for the day, leading us deep below the soil profile to examine the … Read more

B2B 2: the mid-Atlantic phase

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Folks, I’m off to lead another field course – so don’t expect much on the blog this week. This is “phase 2” of the Border to Beltway community college field exchange program. In March, over spring break, I took a dozen NOVA students to Texas to team up with a dozen students from El Paso … Read more

Friday fold: knuckling under in the Mesilla Valley shale

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Here’s a fold I saw in Texas, in the Mesilla Valley shale, close to the contact with the Muleros Andesite at Cristo Rey: This is a pretty wild looking fold. Let’s zoom in on the most deformed portion: Annotation: white is top of the distinctive, blocky, buckled bed, and black is its bottom side. Red … Read more