Mechanization, employment, and output per man in bituminous-coal miningWillard E. Hotchkiss, F. G. Tryon, National Research Project on Reemployment Opportunities and Recent Changes in Industrial Techniques (U.S.), United States. Bureau of Mines · First published 1939Open the Tome
Employment and related statistics of mines and quarries, 1935F. G. Tryon, William Harvey Young, Malcolm Earl Wilson, F. E. Berquist, Maxine M. Otero, Dever C. Ashmead, National Research Project on Reemployment Opportunities and Recent Changes in Industrial Techniques (U.S.), United States. Bureau of Mines, United States. Bureau of the Census · First published 1937Open the Tome
Coal in 1928L. Mann, O. E. Kiessling, F. G. Tryon, United States. Bureau of Mines · First published 1930Open the Tome
