@book{27414,
	author = {Ashley, Geo. H.},
	title = {The undeveloped mineral resources of Pennsylvania /},
	publisher = {Department of internal affairs, Topographic and geologic survey,},
	year = {1933.},
	series = {Pennsylvania. Geological survey, 4th (1919-  ) Bulletin M18-A},
	address = {Harrisburg, Pa. :},
	note = {At head of title: Pennysylvania Geological survey, Fourth series.}
}