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18 April 2014
Here’s what the Sideling Hill road cut looked like last month: It’s a terrific example of a syncline. Usually I show folds in profile view, but here, the view is essentially perpendicular (not parallel) to the axis of the fold: Sideling Hill’s rocks are early Mississippian in age, made of debris shed off the late Devonian Acadian Orogeny, and they were folded during Alleghanian deformation in the Pennsylvanian-Permian.
11 April 2014
My student James O’Brien took this image of a kink band along the Billy Goat Trail, downstream of Great Falls in Maryland’s metamorphic Piedmont province. A lovely little structure, don’t you think? Thanks, James! Happy Friday, all.
4 April 2014
We have a guest Friday fold today, from reader Ben Mackay-Scollay of the Monash University School of Geosciences in Melbourne: Ben writes: Hey there Professor Bentley, been a fan of your blog for a while and I thought you might be able to use this for your Friday Fold series. It’s an upright fold at Bermagui in New South Wales, where I visited recently as part of my post-grad coursework …
28 March 2014
It’s Friday… that means it’s time for a fold. Let’s try this outcrop at “Confusion Hill” in the Franklin Mountains of West Texas: See it? Let’s zoom in… From the shadows to the left of the hammer, trace out the dark green layer… it may make you think of a box fold: …but it’s not. This is actually a completely planar sedimentary bed, tilted to more or less vertical, and …
21 March 2014
I know nothing about this sample, other than the fact that it was a thrown-away sample found in the rock pile next to the old geology building at the University of Texas at El Paso. Happy Friday!
7 March 2014
Happy Friday! Here’s a beautiful folded obsidian sample, replete with conchoidal fractures, on display outside the geology department at Arizona State University in Tempe, where I was last week:
28 February 2014
For the Friday fold, let’s journey back to the Silurian, as exposed in the limestones of that age that were deformed during Alleghanian mountain-building (Pennsylvanian and Permian), and exposed along Corridor H in eastern West Virginia. Some buckling (cuspate-lobate form) seen in that one… A little pop-up with hinge collapse: And, finally, as a digestif, consider this little morsel: That’s a bite-sized Friday fold. Have a good weekend!
21 February 2014
Howard Allen, a blog reader from Canada, digitized a bunch of folds for us from his old Kodachrome slides. You’ll be seeing selections from these images over the weeks to come. Get psyched! There are some great folds in this batch. Here’s the first: Howard’s description: 3D folded marble, Shuswap Metamorphic Complex, north of Sicamous, British Columbia. Specimen was bulldozed out of the way for a logging road. Photographed in …
14 February 2014
Scott Johnson contributed this special “Valentine’s Day” edition of the Friday fold: a lovely primary igneous structure that evokes a heart: That’s a close-up view (lens cap for scale) that Scott took when he GigaPanned this feature: link … the big obsidian flow at Newberry Crater in Oregon. That’s a really dry lava flow that oozed out of the Earth sometime in the past thousand years or so. It’s even …
7 February 2014
I ran out of folds last December, I asked for help on Twitter. Laura Hamilton was among the first to respond, with a link to this image: @callanbentley Hartland Quay, Devon UK. Huuuuge chevron folds! pic.twitter.com/7bhRfLib9Y — lau.rah (@hammijam) December 23, 2013 Thanks, Laura, for another great image!