Factors and conditions that aid in alinement of pillar extraction lines in coal mining

Author:	Geyer, John Nicholas,
Year:	1933
Document Type:	USBI
Issuing Agency:	U.S. Bureau of Mines,
SUDOC:	I 28.27:6727
Series:	Information circular ;
Report Number:	6727
Subjects:	Coal mines and mining--Pennsylvania
	Mining engineering
Link:	https://hdl.handle.net/2027/mdp.39015086486001