12 October 2015
I’ve been thinking lately about Harpers Ferry, the spot where West Virginia, Virginia, and Maryland meet, at the confluence of the Potomac River and the Shenandoah River. I’ve noted small outcrops of its overturned beddding here previously, and also described a book I read about the man who made the place infamous: John Brown.
I went out there again last week with my NOVA colleague Beth Doyle, and we explored some of the geology of the Harpers Formation (early Cambrian on the basis of Olenellus fossils). I made three GigaPan images that day. Here they are:
Link (5.3 Gpx)
The key feature of the first two images is the overprinting relationship of cleavage relative to bedding. Cleavage dips more shallowly to the southeast / right of the photos (~20°) than does bedding (~47°), and this comparison of their orientations may be used to deduce that the bedding has been tectonically overturned during late Paleozoic Alleghanian mountain-building.
Link (3.1 Gpx)
There’s also a spot called Jefferson Rock there, which shows the cleavage very well, and has a fine view (Thomas Jefferson quipped it was “worth crossing the Atlantic” in order to view it), but doesn’t provide as clear a view of the structural relations:
Link (1.9 Gpx)
There were four or five other share-worthy sites that Beth and I saw last week, but the lighting wasn’t perfect for imaging them, or we decided it would be better to wait until some of the foliage dies back in the coming cold season. So I’ll have to go back for those.