@book{34814,
	author = {Van Sant, Joel N. and Ellman, R. C.,},
	title = {Methods and costs of mining lignite in North Dakota,},
	publisher = {U.S. Dept. of the Interior, Bureau of Mines,},
	year = {1959.},
	series = {United States. Bureau of Mines. Information circular},
	address = {[Washington],}
}