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Outcrop Bb25-c: The Yorklyn Railroad Cut

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Rock Outcrop Bb25-c: The Yorklyn Railroad Cut

Wissahickon gneisses and amphibolites are exposed in the railroad cut near Yorklyn. Here the rocks are unusual because the layering is accentuated by the presence of fault gouge between the layers. Fault gouge forms as movement along a fault in hard, brittle rocks crushes and grinds the rocks into a powder. Gouge was a term used by miners because they could easily "gouge" it out of the rock. Here the gouge "weathered out" leaving deep indentations that emphasize the layering and the tilt, which is to the southeast at an angle of about 45 degrees.

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Rock Outcrop Bb25-c: The Yorklyn Railroad Cut.
Rock Outcrop Bb25-c: The Yorklyn Railroad Cut. Note the 45 degree dip of the rock layers to the SE. These layers are in the top limb of the Hockessin-Yorklyn Anticline which is part of the Mill Creek Nappe.
Rock Outcrop Bb25-c: The Yorklyn Railroad Cut.