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17 June 2014

Weathering on Old Rag Mountain 2: Opferkessel

Yesterday, I pointed out an example of differential weathering on Old Rag Mountain, in Shenandoah National Park, in Virginia. Today, I’d like to shine the spotlight on another example of weathering to be seen along the trail there: little weathering pits that occur on the top of the granite outcrops. These are opferkessel. Some people call these “potholes,” a term I do not approve of in this context. To me, …


30 January 2014

Antietam Formation breccia with Fe/Mn oxide cement: 2 GigaPans

One of the intriguing rocks you find in Virginia, at the interface between the Valley and Ridge province and the Blue Ridge province, is distinctive brecciated Antietam Formation. The Antietam (sometimes known as the “Erwin,” especially in Shenandoah National Park), is a quartz arenite (quartz sandstone) that has been variably fused to quartzite in some places (but not others). It’s been deformed, sometimes spectacularly so, as we see when the …


23 April 2013

Return to the Outdoor Lab

Two years ago, I took a trip to the Phoebe Hall Knipling Outdoor Lab, which is Arlington, Virginia’s outdoor education facility in the Pond Mountains (southern continuation of the Bull Run Mountains), on the eastern edge of the Blue Ridge geologic province. I was invited back last week to look at some new exposures. I brought the GigaPan along. There had been additional erosion on the saprolitic exposure of Harpers …


17 April 2013

Four new GigaPans from an intriguing contact

Callan and his colleague Jay Kaufman (University of Maryland) go to extraordinary lengths to document an intriguing block of rock in northern Virginia’s Blue Ridge province. Great images and a lot of fun result – but what do these rocks tell us?


5 April 2013

Two new GigaPans of Rockfish Gap, Virginia

I took a trip down to Charlottesville this week for a couple of meetings, and I made time along the way to capture two new GigaPans of the lovely exposures of Catoctin Formation greenstone at Rockfish Gap, where Interstate 64 traverses the Blue Ridge. This is very close to the southernmost tip of Shenandoah National Park, and at the northern terminus of the Blue Ridge Parkway. The Catoctin is an …


12 March 2013

Five new GigaPans from Thoroughfare Gap

Yesterday, I took five new GigaPans at Thoroughfare Gap, a water gap where Broad Run cuts through Bull Run Mountain, the eastern limb of the Blue Ridge Anticlinorium at my latitude. The rocks here are the Cambrian-aged Chilhowee Group, with bedding tilted moderately to the east during Alleghanian mountain-building in the late Paleozoic. To the west is the crystalline core of this massive regional fold, and to the east is …


8 February 2013

Friday fold: LIDAR view of the Weverton Formation along the Blue Ridge front

Dan Doctor of the US Geological Survey contributed this week’s Friday fold. It’s a lovely view of the asymmetric folds in the Cambrian-aged Weverton Formation (part of the Chilhowee Group, a Sauk-Sea passive margin transgressive sequence), exposed on the western flank of the western limb of the Blue Ridge Anticlinorium. It’s a LIDAR image, and it’s best viewed when draped over the scenery in a Google Earth view. Here’s a …


17 April 2012

Strained Antietam Formation sandstone

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. [gigapan id=”103122″] link It definitely looks best in full screen mode, so please feel encouraged to click through and explore it a bit. You’ll notice some great …


21 November 2011

Compton Peak columns

Callan and three students visit a world-class outcrop of columnar jointing in Shenandoah National Park.


22 June 2011

The Rockfish Conglomerate

Callan presents a gazillion photos from a field trip to examine the Rockfish Conglomerate, a potential Snowball Earth glacial outwash facies from the Neoproterozoic of the Virginia Blue Ridge province.


11 April 2011

Old Rag gigapans

Lily and I took a hike yesterday over Old Rag Mountain, a popular destination in Shenandoah National Park. I took the opportunity to shoot a few gigapan images of the scene. If you click on the word “Gigapan” in the lower right of any of these images, it will take you to’s full page viewer. Once we got above the trees, this was the view to the north: [gigapan …


1 December 2010

The Konnarock Formation

A detailed description of one of the Virginia Blue Ridge’s most intriguing geologic formations: a maroon sedimentary sequence showing the advance of “Snowball Earth” glaciers in the Neoproterozoic.