@book{26889,
	author = {Ashley, Geo. H.},
	title = {A syllabus of Pennsylvania geology and mineral resources /},
	publisher = {Department of internal affairs, Topographic and geologic survey,},
	year = {1931.},
	series = {Pennsylvania Geological survey, 4th (1919-   ) Bulletin G1},
	address = {Harrisburg :},
	note = {"Publications of the present [Pennsylvania] Geological survey": p. 147-150.}
}