Ringing rocks barren block field,East-Central Pennsylvania

Huge residual boulders on and near the surface of the woodlands on the slopes of Coffman Hill probably are corestones of a for derived from the early Jurassic diabase sill. Accordingly, they were produced in two stages - first by chemical weathering along joints before Cenozoic regional uplift, then by exhumation of the blocks during Cenozoic dissection of the old lowland surface.The Ringing Rocks barren block field within the woodlands probably resulted from local mass transport of large boulders from a higher part of Coffman Hill by periglacial creep and solifluction during the Pleistocene epoch. Loss of forest cover and removal of matrix from the patch of boulders exposed the blocks to further mechanical and chemical weathering. Persistent shattering of the boulders along joints and minor movement of smaller derived blocks destroyed any inherited debris-flow pattern. Pitting on the bare joint surfaces has resulted from effective solution by rain in the absence of forest shelter and a mantle of soil. In contrast, exfoliation predominates in the surrounding wooded residual boulder field.