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 … Read more
A virtual field trip to the deformed quartzites and metaconglomerates of Chickie’s Rock and Sam Lewis State Park in Lancaster County, Pennsylvania.
On a family hike, Callan’s son finds some interesting smooth lines on a rock. What are they? What do they tell us? Tune in for a brief history of Appalachian geology.
What does it mean for a vein to be “quantankerous?” Well, to start with, it’s quartz. Second, it has to be disagreeable or cantankerous. This vein, seen in meta-arkose of the Catoctin Formation near the summit of the Blue Ridge at Rockfish Gap (not Afton Mountain), is such a quantankerous individual: You’ll notice its “S” … Read more
Over the weekend, my wife and I took a walk with our son at the Storybrook Trail, an accessible trail with a fine overlook to the east over the Page Valley. There, the Massanutten Sandstone shows a bunch of big beefy trace fossils at this site: both bedding-parallel (Arthophycus-like) and bedding-perpendicular (Skolithos-like) traces. Here’s Bax … Read more
At the Spiral Tunnels overlook on the Trans-Canada Highway, you can look at trains. Or, you can check out some lovely trace fossils in boulders which divide the viewing area from the highway: These are in the Gog Formation, a Cambrian-aged quartz arenite, mostly fused to quartzite nowadays… I know which subject I would choose … Read more
Some boulders seen on the trail to Helen Lake sported lovely sets of Skolithos trace fossils. Here are two boulders, with the perspective on the tubular paleo-vertical Skolithos burrows being “map view”: Another boulder, in the middle of the trail, showed them in a fine cross-sectional view: (click to enlarge substantially) It also included some … Read more
Back in 2011, when we were still living in D.C., Lily and I made a hiking trip out to Buzzard Rocks. It was a destination. Now that I live out here in the Fort Valley, I see Buzzard Rocks all the time, and I love it. It’s such a cool feature – a spot on … Read more
The Friday fold returns to Canada, looking at Neoproterozoic slate and quartzite at the southern terminus of the Icefields Parkway. Bonus features include ripple marks, graded beds, cross-bedding, cleavage, and boudinage.
Today, a few more photos from the field trip last month to Corridor H, the fine new superhighway with so little traffic out in eastern West Virginia. Our antepenultimate stop of the day was at an outcrop we inferred should hold the Oriskany Sandstone, a Devonian quartz arenite that lies stratigraphically above the Helderberg Group … Read more
Hey, that quartzite boulder has measles! Or is it bubonic plague? Or maybe it’s just acne? Look closer and see if you can deduce what these things are: These conical fractures are percussion marks. They form when a cobble smacks into another cobble underwater, propelled forward by a powerful current. As the two rocks knock … Read more
Archaeology meets geology in this visit to the Piney Branch valley of Rock Creek Park in Washington, D.C. Cretaceous deposits of cobbles of Cambrian quartzite were quarried by Native Americans and modified into tools thanks to the fact that they break with a conchoidal fracture.
Here are a few folds in the quartzites of the Cape Fold Belt, exposed on the mountainsides of the Harold Porter Botanical Gardens in Betty’s Bay, South Africa. Hillside #1: Zooming in closer: Annotated (bedding traced out): Hillside #2: Zooming in on summit region: Annotated (bedding traced out): Zooming in on the central portion of … Read more
Geoblogger Siim Sepp contributed this lovely fold. He says: I saw a nice fold in Ireland. I like it because it looks like SS to me which are my initials. If you want, you can post it as your friday fold. I haven’t used it yet in my blog. This small outcrop is in Donegal, … Read more
Concentric ribs with hackles on a joint face, quartzite (metamorphosed fine-grained quartz sandstone stained with hematite) from Waterton Lakes National Park, southern Alberta.
Grab your coffee and join Callan & Lily for a stroll along the quartzite cliffs of Hermanus, South Africa. Bedding, cross-bedding, joints, faults, veins, folded veins, and faulted veins all await you there in the morning light.
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 … Read more
I collected this sample the weekend before last on the Blue Ridge Thrust Fault field trip led by Alan Pitts. It’s a chunk of the Antietam Formation quartz sandstone, a Cambrian beach deposit. The face we photographed measures 15 cm by 12 cm. link It definitely looks best in full screen mode, so please feel … Read more
One of Callan’s former students leads a field trip to examine the western edge of the Blue Ridge geologic province, attempting to answer the question of whether the Blue Ridge / Valley & Ridge contact is indeed the trace of a thrust fault. Breccias and S-C fabrics tell part of the story…
In December, Callan found an outcrop of Neoproterozoic-aged turbidites in South Africa, on the eastern shore of False Bay.