After my thesis defense at the University of Maryland, my mentor and friend E-an Zen asked me if I had ever heard of the Purgatory Conglomerate. I had not. Over the years, E-an has been a great source of new ideas and information to me, and so when he raises a notion, I pay attention. … Read more
Beautiful fiancée for scale.
Mountain Beltway reader Greg Willis attended my colleague Ken Rasmussen’s Triassic Rift Valley field course last weekend, and sent me this photo of the view inside the Luck Stone diabase quarry in Centreville, Virginia: Here’s an annotated version: Both photos are enlargeable by clicking on them (twice). This quarry chews into rock right along the … Read more
The Belt Supergroup is a series of sedimentary strata laid down in the Belt Sea, an inland sea (like modern Hudson Bay) that existed in the northwestern (by present coordinates) part of ancestral North America during the Mesoproterozoic era of geologic time. Estimates of the absolute age of these rocks range from 1470 to 1400 … Read more
There is an old Chinese aphorism that “the beginning of wisdom is to call things by their proper names.” One of the naming conventions that tends to trip up NOVA students who hike the Billy Goat Trail with me is the difference between a “terrace” and a “strath.” This morning, I created a graphic that … Read more
In today’s post, I’ll finish up with my geologic discussion of the falls of the James River in Richmond Virginia, south of Belle Isle. Previously, we’ve examined the bedrock at this location (the Petersburg Granite) and a series of fractures – some faults and some extensional joints – that deform that granite. Now we come … Read more
I mentioned going out in the field last Thursday with Liz Johnson‘s “Geology of Skyline Drive” lab course at James Madison University. We started the trip south of Elkton, Virginia, at an exposure where Liz had the students collect hand samples and sketch their key features. Here’s one that I picked up: Regular readers will … Read more
I took a look at some interesting blobby structures in the Swift Run Formation last week, and walked readers through my logic in tentatively concluding that they were ball & pillow structures (soft sediment deformation), though overprinted by a pervasive (Alleghanian) cleavage. As we move west in the Appalachian mountain belt, the rocks are less … Read more
On my structural geology field trip this past weekend, I made one major modification compared to last year’s iteration. I added a fifth detailed “field study area” at an outcrop of the Swift Run Formation, a Neoproterozoic sedimentary unit that is discontinuous in extent between the underlying Blue Ridge basement complex and overlying Catoctin Formation … Read more
Remember the mud I saw on Pimmit Run? Turns out that West Virginia mud pulls many of the same tricks as Virginia mud. Here’s some mud cracks I noticed on Sunday afternoon on the shoulder of New Route 55 in eastern West Virginia: Notice how West Virginia spices her mudcracks with chunks of Silurian quartzite … Read more