On a birding hike yesterday morning, I found this: This is a little slab of kinked phyllite of the Candler Formation. This metamorphic rock started as mud (and ash) deposited atop the Catoctin Formation, and it was later squeezed and heated during Appalachian mountain-building, encouraging the growth of micas at the expense of clay. A … Read more
Happy Friday, friends. Here’s a rock sample that I recently polished up: It shows crenulations in “pinstriped” schist of the western Piedmont in Pleasant Grove Park in Fluvanna County, mapped as the Mine Run Complex. Lovely stuff, eh?
Callan recounts a little lesson in taking a photograph of an outcrop that expresses itself more readily to the novice eye.
A return to the “video Friday fold” format:
Two weeks ago was the annual Virginia Geological Field Conference, which was centered this year on the Goochland Terrane, an interesting block of crust in the Piedmont which shows some similarities to the Blue Ridge geologic province, but also shows some differences that suggest it’s not just a mini-Blue-Ridge. One of the best exposures was … Read more
A quick Friday fold that I observed last month in a boulder of riprap at Chippokes State Park in Surry, Virginia. I have absolutely no idea where this rock was quarried; but it doesn’t look like anything I’m familiar with in Virginia, so maybe the Baltimore Mafic Complex??? Anyhow, it’s not native to the Coastal … Read more
Exploring his new digs in Charlottesville, Callan is introduced to a large exposure of phyllite at a dam’s spillway. The foliation there is folded in many ways. Share in a dozen field photos of the site…
A summary of resources to learn about the geology of Washington, D.C. and the surrounding region, in anticipation of AGU’s Fall Meeting being held in the nation’s capital city.
Reader and former student Paxton DeBusk shared this lovely folded gneiss with me at the conclusion of the Virginia Geological Field Conference a few weeks ago: That’s a lovely hand sample, with a high folding:volume ratio! Happy Friday, all
It’s been a very Billy-Goaty week for me. Three times since Sunday afternoon, I’ve taken people to the Billy Goat Trail’s “A” loop in C&O Canal National Historical Park. On Tuesday and Thursday, it was my NOVA Physical Geology students. On Sunday, though, it was just my son and me. Good news! He helped me … Read more
It’s Friday! Here’s a lovely sight, contributed by reader Fred Atwood: [youtube_agu id=Au-jIGfbs8g] Those are quartz veins in one of my favorite local rock units, the Mather Gorge Formation. Fred reports, This is at Madeira School in Great Falls between Black Pond and the Potomac. The rocks around Great Falls, particularly those on the Billy … Read more
The Friday fold can be found along the Fall Zone, where crystalline metaigneous rocks of the Piedmont meet the gently sloping strata of the Atlantic Coastal Plain. Contemplate their high metamorphic grade and their tight folding, and imagine the mighty mountains that once rose on this spot.
Alethopteris fern fossil: Link GIGAmacro by Robin Rohrback Rapid River Canyon, Idaho: Link GigaPan by Callan Bentley River cobble of brecciated Columbia River Basalt, Hammer Creek (Salmon River), Idaho: Link GIGAmacro by Callan Bentley Petersburg Granite exposed at Belle Isle, Richmond, Virginia: Link GigaPan by Jeffrey Rollins Ammonite: Link GIGAmacro by Callan Bentley Slickensides in … Read more
As part of my work on the GEODE project, I’m always looking for good imagery to teach key concepts in geoscience. One important concept that I’ve been thinking about lately is the principle of relative dating on the basis of inclusions. Just as you can’t bake a loaf of raisin bread without already having raisins … Read more
My friend Barbara am Ende sent along this lovely image of a dike in Colorado: Here’s the site. You can see the dike in Google Earth. Dikes are fractures, filled with molten rock, which then cools and solidifies, sealing the crack shut. In this case, once it got uplifted to Earth’s surface and exposed, the … Read more
What hath the Potomac River wrought on the rocks of Mather Gorge? Some interesting shapes to the land surface reveal a fascinating history.
What is Kenny pointing at here? Why, it’s a boulder. Where did it come from? Look uphill: This is as perfect an example of root wedging as I’ve seen! Spotted it last Friday along the C&O Canal towpath.
Here are four folds from the Potomac Terrane (or maybe an “exotic unit” that looks like the Potomac Terrane, butted up against the Potomac Terrane) that I saw on the 2014 Virginia Geological Field Conference back in October. It was an overcast, rainy day, so I apologize for the relatively low quality of these images. … Read more
Last week, the “Border to Beltway” field exchange team went to Dora Kelly Park in Alexandria, Virginia. There, a ravine reveals the boundary between the Coastal Plain and the underlying metamorphic rocks of the Piedmont… My NOVA colleague Ken Rasmussen joined us for the day, leading us deep below the soil profile to examine the … Read more
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.