Excerpt from The Coal Fields of the United States: General Introduction In anticipation of this action the Geological Survey had begun in 1905 the systematic ex amination of coal fields in the public-land States and by 1908 had made sufficient prog ress in that work to issue the first reasonably accurate map of the coal fields Of the country, on a scale of about 120 miles to the inch. In addition to outlining the coal fields, this map differentiates the areas of known coal from the areas that might possibly contain valuable coal and shows also those areas in which the coal-bearing rocks are under deep cover. On this map the coal fields are classified according to the rank of the coals they contain, or at least three great groups are recognized, namely, (1) anthracite, semianthracite, semibituminous, and bituminous coal; (2) subbituminous coal; and (3) lignite. In addition to delineating the coal fields, the map contains an estimate of the tonnage of coal still remaining in the ground and supposedly available for the future needs of the country. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.