Cretaceous Period

(-tā'shus.) [From L. creta, chalk.] (Geol.) The upper strata of the secondary series,immediately below the Tertiary beds, and resting on the Oolite. This group is separated from the Eocene Tertiary beds by a decided change in the rocks and fo ils, many genera of mollusks and reptiles finishing with it, while modern types of plants and fishes make their appearance in it. The most remarkable petrological characteristic of this group is the chalk, which exists in Europe in such abundance as to have given its name to the formation. The strata of the C. P. have been arranged in the following order. The maximum thickne of the division is given in feet. Maestricht andFaxoe, 100 feet. White chalk with flints 500 66 White chalk without flints.. 600 66 Upper. Chalk marl.... 100 " Upper greensand 100 “ Gault 150 " Lower greensand 850 " Lower. 66 Wealden beds 1,300 In N. America the C. beds occur at intervals along the Atlantic border from N. York and N. Jersey to S. Carolina, extending over the States along the Gulf border,and through a large portion of the Western interior region, over the slopes of the Rocky Mountains, from Texas northward, to the head-waters of the Mi ouri, and further N.W. into British America. The rocks comprise beds of sand, marl, clay, loosely aggregated shell limestone, and compact limestone; but they include no chalk. [s. 243]