@book{26880,
	author = {Swartz, Frank M.},
	title = {The Helderberg group from central Pennsylvania to southwestern Virginia,},
	publisher = {State College, Pa., School of mineral industries,},
	year = {1929.},
	note = {[pt. 1] "reprinted from the Proceedings of the Pennsylvania academy of science, v. 3, 1929."}
}