Lewis, R. S. (1939). Mining, the priceless heritage. Extension Division, University of Utah.
Lua i Stíl Chicago (17ú heag.)Lewis, Robert S. Mining, the Priceless Heritage. Salt Lake City: Extension Division, University of Utah, 1939.
Lua MLA (8ú heag.)Lewis, Robert S. Mining, the Priceless Heritage. Extension Division, University of Utah, 1939.
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