@book{26809,
	author = {Bownocker, J. A. and Campbell, Marius R.},
	title = {The coal fields of the United States.},
	publisher = {U.S. Govt. print. off.,},
	year = {1929.},
	series = {U.S. Geological survey. Professional paper},
	address = {Washington,},
	note = {At head of title: Department of the interior.}
}