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Some Observations as to Safety Hazards in 47 Northern Colorado Subbituminous Coal Mines

Edward H. Denny

出版	U.S. Department of the Interior, Bureau of Mines, 1935
URL	http://books.google.com.hk/books?id=wKriiBhDbHEC&hl=&source=gbs_api
EBook	FULL_PUBLIC_DOMAIN