Shaft sinking by stripping churn-drill holes

Author:	Cole, W. A.
Year:	1945
Document Type:	USBI
Issuing Agency:	U.S. Dept. of the Interior, Bureau of Mines,
SUDOC:	I 28.27:7308
Series:	Information circular ;
Report Number:	7308.
Subjects:	Shaft sinking
	Mine shafts
Link:	https://hdl.handle.net/2027/mdp.39015074127443