GEOLOGY AND MINERAL RESOURCES. The Medicine Bow, Laramie, Big Horn, and Wind River ranges have their cores of Archaean crys talline rocks exposed along their crests. These outcrops are flanked by narrow bands represent ing the upturned edges of Paleozoic and Lower Mesozoic strata in a regular series from Cambro Silurian to Jura-Trias. On the latter rest the Cretaceous strata, which form the surface rock of the Cheyenne, Powder River, Wind River, and Laramie basins. The southwestern plains and the Big Horn Basin are covered with Eocene de posits, and the southern part of the Platte Basin, east of the Laramie range, is covered with the later Tertiary deposits of the Great Plains for mation. The Yellowstone region, in the north west, is volcanic, and consists largely of lava flows. The mineral wealth of Wyoming is very extensive and varied, and gives promise of great future development. Copper and lead ores asso ciated with silver exist in every range, and gold is also found in numerous localities. Red hema
tite iron ores are deposited on the southeastern slope of the Laramie range, hut the most im portant mineral at present is coal, of which there are a number of large fields, chiefly in the south western part of the State. Each field contains several workable veins ranging from pure lignite to good bituminous, and in some localities even to a semi-anthracite. Great bands of bituminous shale exist in the Green River Valley: and in the central part of the State, as well as in several other localities, there are a number of petroleum and natural gas fields, some of which come natu rally to the surface as petroleum springs. Large veins of graphite and some asphaltum deposits occur in the oil region. Other minerals are as bestos and gypsum. the latter occurring in great quantifies. while building stones exist in im mense variety and inexhaustible amounts.