NOTES FROM Maryland Geological Survey Vol. Ix Stratigraphy (C.K.Swarty & G.M.Hall, p337-) Permian Greene Washington Pennsylvanian Monongahela Conemaugh Allegheny Pottsville Mississippian Mauch Chunk Greenbrier Pocono 'group' (Eastern coal basins) Pinkertan ss. Myers sh Hedges sh Purselane ss Rockwell sh Fire clays. (Restricted to Allegheny) Pottsville - none, Mercer consists of shale with upper and lower coals. Pottsville section :- Homewood Mercer Connoqueening (upper + lower with Quakertown shale + coal between) Sharon (shale, coal, ss in this order?) Allegheny - 5 fire clay horizons, 4+, 1-. Conemaugh - (Thornton Clay - associated with Mahoning red shale. Basically Monongahela - no commercial clays.