E'OCENE EPOCH (from Gk.ficiis, cos, dawn + mobs, k.a-inos, new). A division of geologic time following the CretaceOns period and mark ing the beginning of the Cenozoic era. At the end of the Cretaceous period great geographical changes occurred in both Europe and North America, by which the floor of the inland seas was raised partly into land and partly into shal low waters. This elevation took place slowly and occupied a long interval of time, so that when the Eocene period opened the fauna and flora had assumed a decidedly modern aspect. Among in vertebrates the ammonites, which were character istic of the Mesozoic era, became extinct, while bivalves, such as the oyster, clam, and scallop, common at the present day, were very numerous. Ganojd fishes became subordinate to the teleosts, which included perch, herring, and sharks, and mammals predominated over reptiles. In rocks of this period have been found the remains of `eohippus,' the earliest-known direct ancestor of the horse. The vegetation included dicotyls, palms, and grasses belonging to genera living at the present time. Eocene rocks in the United States arc found along a belt that extends par allel to the Atlantic coast from New Jersey to Florida, in the Mississippi Valley, in the Gulf States, and in California, Oregon, and Washing ton. There are numerous basins also in the
Rocky Mountain region of Utah, Wyoming, Col orado, and New Mexico, which, unlike the preced ing. were deposited in fresh water. The most im portant of these basins are the Puerco, Wasatch, Green River, and Uintah. In the Uintah basin the deposits are 6000 to 8000 feet thick. The following division of the Eocene is recognized by American geologists: Atlantic and Gulf States: (a) Midway, (b) Lignitic. (c) Lower Claiborne, (d ) Claiborne, ( e) Jackson, ( f ) Vicksburg Western States: (a) Puerco, (b) Wasatch, (e) Wind River, (d) Bridger, (e) Uintah. The rocks of the Eocene include clays, sands, lime stones, and sandstones, while among the economic minerals are marls in the Atlantic States, phos phate rock in Florida, and brown coal in Nevada. Consult Geikie, Text-Book of Geology (London, 1893). See TERTIARY SYSTEM ; GEOLOGY.