USGS1953
As estimated in this second progress report, the coal reserves of the United States remaining in the ground on January 1, 1953, total 1,899,739 million tons. This figure is about a 20 percent reduction of the total estimate published in the first progress report (Averitt and Berryhill, 1950). The new total is based on new, detailed, conservative estimates of reserves in Indiana, Michigan, Montana, New Mexico, North Carolina, North Dakota, South Dakota, Virginia, and Wyoming, prepared since 1947 by the U. S. Geological Survey; on new provisional, but equally conservative estimates of reserves in Colorado, Maryland, and Georgia, based on previous work of the U. S. Geological Survey and other agencies; on estimates of reserves in Illinois, Kansas, Pennsylvania, and West Virginia, prepared by the geological surveys of those States; and on older and incompletely documented estimates for the remaining states. The older estimates were prepared on a highly generalized basis and were intended to represent total possible reserves in both thick and thin beds and under both light and heavy overburden. The recent estimates have been prepared on a more conservative basis than the older estimates and tend to be considerably smaller. New conservative estimates have now been prepared for 16 coal-bearing States, which include about two-thirds of the total estimated reserves of the United States. As new estimates are prepared for the remaining States a further reduction of the total reserve figure is in prospect, though the reserves still will be large. The estimated recoverable reserves of the United States as of January 1, 1953, total 949,870 million tons, based on the assumption that half of the coal reserves in the ground will be lost in mining, and half will be recovered. The distribution of the remaining and recoverable reserves by rank is shown in the accompanying table. The reserves in 10 States have been classified in considerable detail according to thickness of beds, thickness of overburden, and relative abundance of reliable information available for making estimates. In these States, which are representative of several coal provinces, and contain about 40 percent of the total reserves, and are thus typical of the United States as a whole, 5 percent of the total is measured reserves in beds 28 inches or more thick, and less than 1,000 feet below the surface; and 20 percent is indicated reserves within the same limit of thickness and less than 2,000 feet below the surface. The remaining 75 percent is inferred reserves, reserves in thin beds, and reserves 2,000 to 3,000 feet below the surface. The large percentage of inferred reserves obviously includes some coal in thick beds, which for lack of detailed information cannot be appraised quantitatively. Although accurately based on the data now available, the distribution percentages are subject to considerable change as new work is completed, particularly in the transfer of reserves from the indicated and inferred categories to the measured category. The figures serve, however, to indicate the present state of knowledge of the Nation's coal reserves, and they point to the need for additional geologic mapping and exploration.