Costs of mining under bolted roof and timbered roof in bituminous coal mines / by M.J. Ackerman and J.J. Wallace.
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| Format: | Government Document Book |
| Language: | English |
| Published: |
Washington, D.C. :
U.S. Dept. of the Interior, Bureau of Mines,
1961.
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| Series: | Information circular (United States. Bureau of Mines) ;
8024. |
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