13 November 2020
This Friday fold is a bed of Tonoloway Formation dolostone, from a pile of scree below a roadcut in Grant County, West Virginia, on Corridor H. It’s got two lovely “stairstep” style folds superimposed on it.
I love folds that are expressed in three dimensions. Very satisfying.
9 October 2020
Looks like we’re sticking with the U.K. for Friday folds, for the time being…
This lovely beast comes to us from Torcross, via Danny Stubbs, who shared it on Twitter this past week.
That’s from the Meadfoot Group of slates, cross-cut by quartz veins.
In this follow-up image, Danny shares that sometimes the quartz veins have enjoyed some folding too:
Happy Friday to all.
2 October 2020
For the Friday fold this week, we travel to Northumberland, U.K. for this beautiful fold pair:
Robert McKibbin posted this image on Twitter this week, and graciously allowed me to feature it here.
Thank you Robert!
Happy Friday to all.
18 September 2020
Working up some new images for my free, online Historical Geology textbook, I annotated a photograph I took in March of this alluvial fan in southern Death Valley. The development of desert varnish on older parts of the fan shows their age visually in a quick and easy way of determining fan deposit sequence:
I’ve been making a lot of these animated annotations as a way of conserving space in the “real estate” of the online text’s pages.
Happy Friday. Back to folds next week!
11 September 2020
These images come from Lilly Wilson, an undergraduate geology student at the University of Bristol:
Here’s her original tweet, which has 4 images:
Boscastle, Cornwall is home to some of the most spectacular folding and quartz veins I’ve seen. Every hillside you look there’s a new array of mangled rocks from the Variscan Orogeny! pic.twitter.com/B9tIkvBxna
— Lilly Wilson (@D1amondsR4ever1) September 9, 2020
For my American readers, the Variscan is the European equivalent of the Alleghanian Orogeny in the Appalachian mountain belt. At the same time these rocks were being deformed, similar strata were experiencing similar folding in my backyard.
Lilly should also be commended for her choice of field assistant, who appears to be a shrewd judge of structural geological character:
Great rocks, excellent photos, and a thoughtful pooch, too – excellent tweeting! Thanks for sharing, Lilly.
Happy Friday all!
4 September 2020
Busy weeks lately; apologies for the minimal bloggery, friends.
For this week’s Friday fold, I offer you a view of some of the outdoor decorations at our new house:
In the lower basket there is a cut and polished block of Castile Formation rock gypsum + limestone, showing varves that have been folded, apparently by hydration/dehydration volume changes of the gypsum/anyhdrite laminae:
This is from the State Line outcrop on the border of Texas and New Mexico in the legendary Permian Basin. I collected it during the epic “Border to Beltway” field trip that Joshua Villalobos of El Paso Community College and I co-led something like seven years ago…
Happy Friday to you. I’m headed into the field today to track down some mylonite. Be well.
11 August 2020
I recently finished two books that feel “of a piece.” Here is a combined review, and I’ve thrown in a review of a similar book too, as a lagniappe.
The Book of Eels, by Patrik Svensson
This new book recounts the amazingly hidden world of the European eel, with digressions into American eels and Japanese eels. It alternates chapters focused on science and the history of that science with chapters of reminiscence, where the author recounts eel fishing with his father, and ties the history of his family in Sweden with key aspects of eel biology. It’s a personal memoir about his father, and at times it seems like Svensson is losing the thread with too much family focus, but eventually it always loops back around to the mystery of the eel. And they are mysterious indeed. The animal goes through four metamorphoses during its life, after being born in the Sargasso Sea, then finding its way to Europe across the wide Atlantic, working its way up a freshwater stream, and establishing itself inland for years, perhaps decades, and in several cases, for probably more than a century, before returning to the sea and spawning. These different body plans are so distinct that for a while, they were thought to be separate species. A fun chapter in the book recounts young Sigmund Freud’s fruitless summer of dissecting eels in Trieste, searching for the testicles of one of the pre-reproductive life stages. Another fascinating chapter recalls the heroic decades-long effort by Johannes Schmidt to trace leptocephalus eel larvae to their source, scouring the ocean for smaller and smaller specimens. It was because of this work that biologists have come to the conclusion that the Sargasso Sea is the birthplace of the eel. But no one has ever observed adult reproductive eels in the Sargasso Sea. Never, not alive or dead. Do they actually spawn there? No one has every actually observed eels spawning at all. This is part of the mystery. It’s compounded by the eels’ decreasing numbers. In half a century, they have gone from a reasonably common foodstuff to a critically endangered species.
The Secret Life of Lobsters, by Trevor Corson
Speaking of animals we eat, consider the lobster. Trevor Corson did, in this 2005 book. As with The Book of Eels, Corson’s book combines personal history with the story of scientific insights about the lobster in the Gulf of Maine. Corson gives equal weight to the stories of lobstermen and biologists, describing the arcs of their lives as well as the insights they generate about the behavior of the chunky crustaceans. My favorite story is that of Diane Cowan, who was so lobster obsessed as a young scientist that she took a lobster experimentalist job without pay or a place to live, just so she could focus her attention on lobsters as much as possible. Her experiments with captive lobsters in tanks revealed key information about the way lobsters mate and balance their social lives. She eventually landed the job of chief lobster biologist for the state of Maine, but quit because she found it didn’t provide her enough time with lobsters! Both Corson and Svensson tell the stories of their scientist subjects well, but Corson’s book comes away feeling more person-focused, while Svensson’s attention is wonder-focused on the eels.
These two books reminded my of a worthy third, which I recently re-read. So I republish here my review of that volume, on octopuses, for the sake of rounding out a trilogy of watery animal profiles:
Other Minds, by Peter Godfrey-Smith
The Octopus, the Sea, and the Deep Origins of Consciousness is the subtitle of this fascinating, extremely approachable book. Paraphrasing Thomas Nagle, it asks “What is it like to be an octopus?” The author is a philosopher by training, but he does a fantastic job as a science writer, too. Anecdotes about encounters with cephalopods while diving are mixed with careful, deliberate, dejargonized descriptions of the scientific studies that have illuminated the evolution of minds. While we know that dolphins and chimpanzees and parrots are smart, they are all united in being vertebrates with a similarly-organized nervous system. Cuttlefish, squid, and octopuses are however much more distantly related (we share a common ancestor something like 550-600 million years ago), and yet they have independently evolved a remarkable intelligence. Like us, they have large nervous system and camera-like eyes, and they play, solve puzzles, and are able to recognize specific individuals (both among octopuses and humans). Unlike us, they have almost no skeletal material, most of their neurons are in their tentacles (essentially, “eight large, flexible lips”), and what amounts to a brain is roughly donut-shaped and has their digestive system pass straight through its middle! They are weird – as alien a natural being as we are likely to ever encounter.
Godfrey-Smith describes the evolution of minds from the very earliest signalling behavior in bacteria, drawing from molecular genetics, developmental biology, ethology, and paleontology. He spends a delicious chapter among the Ediacara fauna en route. In plain terms, he illuminates what a nervous system is good for. He reveals that which is hiding in plain sight: that our nervous systems can partially operate independently of direction from our brains, and argues that octopus tentacles may well be said to “think” for themselves. He dives deep into the remarkable color/texture manipulation of the skin in these cephalopods, and the evolutionary pressures that led to their woefully short lifespans (most octopuses are dead by two years of age). He explores the possible beginnings of octopus culture at a site off the coast of Australia, and speculates how unusual social living might drive octopus mind evolution in new directions. All told, I found it to be a heartfelt, insightful book.
7 August 2020
I went on a day of field work last week to Corridor H, West Virginia, to help make drone-based photogrammetric 3D models of the huge outcrops there. One site we stopped at is this beautiful V-shaped syncline in Devonian-aged Helderberg Group limestones.
Here are two layers traced out:
Here is a GigaPan that Alan Pitts shot of this outcrop several years ago, when it was a bit fresher, and in a different season, to boot. You’ll note some significant differences in comparing the two views!
Happy Friday to you. Today marks one week of residence at my new house in the hills north of Charlottesville; we’re finally starting to feel settled in. I hope you are well.
31 July 2020
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:
And here it is in Google Maps, with the perspective rotated to looking ~along strike to the north, and I hope you will note that (1) this anticline is not alone: there are at least four big folds here, 2 anticlines and 2 synclines, and also that (2) there are similar expressions of these folds in the ridges both north and south of the one I spotted.
There’s a ton of folds there! And based on their position in the landscape, I’m guessing this is all Antietam Formation, which should mean it’s chock full of bedding-perpendicular Skolithos trace fossils: poles to bedding for the structural geologists, I reckon. Someone should map this area in detail…
24 July 2020
I have moved from the Fort Valley to Charlottesville, Virginia, where next month I’ll take up a new position teaching geology at Piedmont Virginia Community College. I’m excited to be in a more progressive community with excellent food and music, and a wealth of new outdoor recreational opportunities – not to mention higher-performing public schools for my son.
But what about the rocks? I don’t know the rocks around here yet!
This is the first post of what I hope will be many, as I explore my new home region and learn about its diverse geology. Charlottesville sits at the interface between the Blue Ridge and Piedmont geologic provinces, with Triassic rift basins located a short distance along strike to both the northeast and southwest. Surely there will be lots to see and learn! Where to begin, though….?
I’m fortunate to have several friends in town, and this past week, one of them showed me a cool outcrop of phyllite. At the spillway for a dammed reservoir on Totier Creek, north of the James River near Scottsville, the outcrop is much cleaner and less vegetated than many central Virginia sites. It pleases me to find clean rocks outside!
Because of being periodically scoured by overflow from the reservoir, the outcrop here is pretty clean, with sparkling silver outcrop where the water is rushing over it…
…and nearby dry locations shining with a muscovite gleam:
…but the same rocks show a rusty patina at less frequently scoured locations…
… and lichen encrustation at the most infrequently-scrubbed sites:
And the foliation is folded in a bunch of different styles – open, undulating folds, tight kinks, and combinations thereupon:
Depending on the map you consult and how willing you are to extrapolate along strike, this site is mapped as “ꞒZpm- metagraywacke, quartzose schist and melange,” “ꞒZmg – metagraywacke,” or Pzc – Candler Formation – muscovite-chlorite-quartz-paragonite phyllite and schist, metagraywacke.” I found my visit there to be intellectually stimulating, despite oppressively brutal heat. But these were new rocks, and visiting the Totier Creek spillway was the first step toward a new appreciation of a new regional geology.
All told, there was a good amount to see, and I can envision some fun student projects to be conducted at the site: for instance, “Does the orientation of the maximum principal stress implied by the veins match that implied by the kink fold axes? If not, which one came first?” Or using the weathering levels to map out scouring histories of different parts of the outcrop; perhaps augmented by some lichenometry?
It’s exciting to think about the possibilities… hopefully our nation will be able to get this pandemic situation under control so that someday I can actually plan for field trips with students again.