N:
National Coal Resources Data System - US Coal Resource Database (USGCOAL) - Searchable database for locating information on coal resources by area, coalfield, coalbed, rank, quadrangle, source, years, or characteristics of thickness, overburden, and reliability. [U.S. Department of the Interior (DOI), U.S. Geological Survey (USGS)]

R:
Record Group 150: Records of the National Bituminous Coal Commission, 1919 - 1936 - National Archives' Archival Research Catalog description for Record Group 150: Records of the National Bituminous Coal Commission, 1919 - 1936 [U.S. National Archives and Records Administration (NARA)]

Record Group 222: Records of the Bituminous Coal Division, 1937 - 1943 - National Archives' Archival Research Catalog description for Record Group 222: Records of the Bituminous Coal Division, 1937 - 1943 [U.S. National Archives and Records Administration (NARA)]

Record Group 223: Records of the Office of the Bituminous Coal Consumers' Counsel, 1935 - 1943 - National Archives' Archival Research Catalog description for Record Group 223: Records of the Office of the Bituminous Coal Consumers' Counsel, 1935 - 1943 [U.S. National Archives and Records Administration (NARA)]

Record Group 68: Records of the U.S. Coal Commission, 1896 - 1927 - National Archives' Archival Research Catalog description for Record Group 68: Records of the U.S. Coal Commission, 1896 - 1927 [U.S. National Archives and Records Administration (NARA)]