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25 December 2023
The Greywacke, by Nick Davidson
Just finished a geologically focused book that the readers of this blog might be interested in. It is a history of work on delineating the early part of the Phanerozoic timescale in Wales and Scotland. The majority of the book is about Adam Sedgewick and Roderick Murchison and their close collaboration and increasing divergence and eventual total estrangement as they sought to sort out the boundaries of different periods of …
16 August 2022
Kinked metavolcanics of the Castine Formation, eastern Maine
Callan shares a few outcrops from coastal Maine, part of the Avalonia terrane that accreted to ancestral North America during the Acadian Orogeny. They are volcaniclastic rocks, coarse and fine, and showing both overprinting kink bands and cross-cutting basaltic dikes.
31 July 2020
Friday fold: Two Mile Run Overlook
I spied an anticline last weekend while engaging in a day of solo geologizing along Skyline Drive in Shenandoah National Park. At Two Mile Run Overlook, I gazed west toward the southern tip of Massanutten Mountain, and noted what appeared to be an anticline in the Blue Ridge foothills: Annotated: And here it is in Google Maps, with the perspective rotated to looking ~along strike to the north, and I …
14 June 2019
Friday fold: kinked cleavage at Harpers Ferry
Last weekend was the annual meeting of the eastern section of the National Association of Geoscience Teachers. On Friday afternoon, we visited Harpers Ferry, West Virginia, and my colleague Beth Doyle led a great field trip to examine the rocks exposed there. This was my favorite outcrop we saw: Here is a close up of this outcrop, which is framed by (anthropogenic) rock wall: Dipping shallowly from upper left to …
9 June 2018
Friday fold: contorted carbonates of the Conestoga Formation
Today, in Millersville, Pennsylvania, on the campus on Millersville University, I saw these contorted carbonates. They are of the Cambrian Conestoga Formation, and I saw them on a NAGT Eastern Section field trip led by Lynn Marquez of Millersville University. This deformation is purported to be Taconian, but it looks very much like Alleghanian deformation in similar aged and composition rocks in Virginia. Interesting!
30 March 2018
Friday fold: Recumbent Harpers
Stop the presses! This late-breaking Friday fold has just been submitted here at Friday Fold Headquarters. This is from Philip Prince/Virginia Division of Geology and Mineral Resources: It’s a recumbent fold of Harpers Formation metasandstone in the James River Face area. Pretty lovely exposure. This outcrop would make a good 3D model. Happy Friday to all. Hope it’s a good one!
1 March 2018
A GIGAmacro view of a cool outcrop in Scotland
As noted previously, the old way of viewing gigapixel imagery is no more. But there is a new, better way. The GIGAmacro company has a better viewing platform that can be used either with images uploaded to their server or with pre-existing images that currently “live” at GigaPan.com. Here’s an example: a roadcut of limestone of the Grudaidh Formation (Durness Group) in the Northwest Highlands of Scotland, near Ardvreck Castle, …
16 June 2017
Friday fold: toothpasty Tomstown
I spent last weekend at the National Association of Geoscience Teachers’ Eastern Section meeting, based out of the Community College of Baltimore County in Catonsville, Maryland. One of the two field trips I took headed out to the western Piedmont, Blue Ridge and Valley & Ridge provinces of western Maryland. On that trip, we took a tour of Crystal Grottoes, a commercial cave south of Boonsboro. I was impressed at …
5 May 2017
Friday fold: sea monster in stone
It’s Friday, the end of the workweek, but also the beginning of the celebration of folded rocks. Examine a particularly sinuous example from the buckled Cambrian limestones of Canada’s Kootenay National Park.
20 September 2016
A virtual field trip to examine the Peninsula Sandstone on Table Mountain
Take a virtual field trip to Table Mountain, near Cape Town, South Africa. Digital media to explore from the site include: a 3D model, 3 GigaPans, and a 360° spherical photo!