You are browsing the archive for 2012 May.
17 May 2012
Yesterday, I introduced percussion marks to this blog space. Here are some other shots of this distinctive “shatter” structure, but in a vein of hydrothermal (milky) quartz exposed on Bear Island, between the C&O Canal and the Potomac River (about right here, just west of the trail): Sometimes percussion marks are accompanied by radial fracture sets like this one… I interpret these radial fractures (sometimes with small cone-fractures at the …
16 May 2012
One of the ~350 or so blogs I subscribe to is Arctic Sea Ice by Neven. Today, he put up a post highlighting new daily data from IARC-JAXA, a collaboration between the International Arctic Research Center (IARC) at the University of Alaska-Fairbanks and the Japan Aerospace Exploration Agency (JAXA). Check it out. Here’s a couple of things I was struck by: The annual variation between summer and winter ice cover …
Further upstream from the Skolithos and the snake and the diabase rip-rap… The field review team wandered down onto a creekside outcrop of Antietam Formation. The Antietam is a quartz sandstone, with variable levels of deformation, depending on where you look. In some places, it has been gently strained with the little Skolithos tubes taking on elliptical cross sections, or the individual sand grains undergoing a moderate amount of pressure …
15 May 2012
Seen in rip-rap on the side of Naked Creek, a week ago yesterday: This boulder is exotic to its current location. It is typical of medium- and coarser-grained diabase from the Culpeper Basin, a Triassic rift valley east of the Blue Ridge. The main minerals are plagioclase (light-colored) and pyroxene (dark colored).
14 May 2012
Callan and his wife hike Cory Pass in Banff National Park, Canada, and encounter some geology, some solitude, and a spectacular landscape.
13 May 2012
The word “Shenandoah” is thought to mean “daughter of the stars,” a lovely turn of phrase even if there’s no evidence for it. The name has been applied to a variety of features in the Commonwealth of Virginia. One is the Shenandoah River, and the valley in which it flows. Here’s a look at the North Fork of the Shenandoah, northwest of Massanutten Mountain: Then there is the political entity …
12 May 2012
Handwritten notes by Ernst Cloos (legendary structural geologist from Johns Hopkins University) on the area I visited last Monday on a field review of the new geologic map of the Elkton East quadrangle by Chelsea Jenkins, Chuck Bailey, Mary Cox and Grace Dawson.
11 May 2012
Max Arndt contributed this week’s Friday fold: (click on the image to get to a larger sized version on Max’s Flickr page) That’s the Warah Formation exposed on the Batain Coast of northeastern Oman. This is the thrust front of a thin-skinned fold and thrust belt. I think it’s just lovely! Max has a ton of other great structure photos on Flickr, he tweets, and he has a blog. Check …
10 May 2012
As I mentioned, Monday had me out in the field, looking at the western Blue Ridge and eastern Valley & Ridge provinces in Virginia. This was a field review for the new geologic map of the Elkton East quadrangle by Chelsea Jenkins, Chuck Bailey, Mary Cox, and Grace Dawson. Immediately after lunch, we visited an outcrop in the middle of Naked Creek. You’ll be happy to hear that we all …
9 May 2012
Saw this fellow on Monday, coiled up next to an outcrop of Antietam Formation in Naked Creek, northwest of Elkton: It had flattened its head to make it very spade-shaped. The right eye was cloudy – perhaps snake glaucoma? Or maybe it was just getting ready to shed its skin?