Pressure-Solution Cleavage

Slaty cleavage (oriented parallel to red line) resulting from pressure solution in the Martinsburg Slate, Belvidere, New Jersey. The pressure-solution origin of the cleavage is based on the offset of the vein material along cleavage surfaces (good examples are pointed out by the light blue arrows). The vein material originally formed parallel to the bedding, was asymmetrically folded, with many of the short limbs of the fold removed by pressure solution. See sketch. Bedding at this outcrop (yellow line) dips more steeply than cleavage and in the same direction as cleavage, indicating that bedding is overturned. This outcrop is a stop on the Valley-and-Ridge field trip. Photo credit: Roy W. Schlische.