Esteemed readership, I’ve got a mystery for you. What are these white lines, inclined consistently at a high angle to bedding? I picked up this sample below the “Wall of Death,” on the trail from Wapta Lake below Mount Wapta, en route to the Walcott Quarry of the Burgess Shale. The “zebra-striped” rock is of … Read more
Over the weekend, I ran a 1-credit field course for NOVA, on the geology of Shenandoah National Park. I was about eight minutes early getting to the meet-up location, so that allowed me to check out a promising new outcrop of rock along the road (route 33, ~100 m west of Swift Run Gap). Here … Read more
As noted previously, I live in a regional scale fold: the differential erosion of the Massanutten Synclinorium has produced the ridge of Massanutten Mountain, which separates the Fort Valley from the Shenandoah and Page valleys on either side. The Fort is “fort” like because the strata which underlie it are relatively friable, soluble, or otherwise … Read more
Howard Allen returns with a Friday fold contribution for this week. He says: Not exactly a fold, but I thought you’d like this rolled boudin(?) (quartz) in a muscovite garnet schist (note garnets above the lens cap). This specimen is also from the Shuswap Metamorphic Complex, north of Sicamous, British Columbia. Lovely. Thanks for sharing, … Read more
We visited the Philip Carter Winery this weekend with family. Baxter and I were pleased to see outcrops of charnockite scattered over the property (located in the middle of the Blue Ridge geologic province). As any 18-month-old will tell you, charnockite is a pyroxene-bearing granitoid. It’s a distinctive and common rock type in Virginia’s Proterozoic … Read more
While we’re out on Corridor H, let me show you some new halite casts I found (either the Wills Creek Formation or the Tonoloway Formation): Salt casts are among my favorite primary structures. They speak very specifically to hypersaline depositional conditions.
While at the University of Texas at Austin, where the Jackson School of Geosciences was hosting the Summit on the Future of Geoscience Education this past weekend, I was impressed to see a well-developed rock garden outside the student center. Here’s an example of a stretched-pebble conglomerate from that garden: Note the nice epidote boudins … Read more
Some ice seen this morning, the coldest we’ve yet experienced at our home in the Fort Valley… 4° F when we got up this morning, with windchill around -15° F. Frost nucleated on a “petal” from a tulip tree (Liriodendron tulipifera): Frost on grass (note the different habit of the ice crystals here): Frost on … Read more
Yesterday we examined primary sedimentary structures (including trace fossils) at an outcrop of Devonian-aged Brallier Formation turbidites between Deerfield and West Augusta, Virginia. Today, we’ll zoom in on the tectonic structures at the site: folds, faults, and joints. Remember, you don’t have to take my word for it. You can explore it for yourself in … Read more
Following on yesterday’s post about the kink bands within the strained metagraywacke of the Laurel Formation in DC, let’s take the opportunity today to go to Klingle Valley, site of a different facies within the Laurel Formation: a strained metaconglomerate. Though the exposure isn’t as great as the Purgatory Conglomerate, I think you’ll find plenty … Read more