http://pec.lib.wvu.edu/record/P4561879Surface geology of south-west Pennsylvania and adjacent portions of West Virginia and Maryland.Journal article tearout from: Proceedings [of the] American Philosophical Society, v.18:no.104 (1879:Sept.) Paper read "before the American Philosophical Society, August 15, 1879."Stevenson, John J. (John James), 1841-1924.Geology--Maryland.Geology--Pennsylvania.Geology--West Virginia.14256