@book{27501,
	author = {Grim, Ralph E. and Allen, Victor T.},
	title = {Petrology of the Pennsylvania underclays of Illinois,},
	publisher = {Printed by authority of the state of Illinois,},
	year = {1938.},
	series = {Illinois.  State geological survey.  Report of investigations},
	address = {Urbana, Ill.,},
	note = {cover title.}
}