Cretaceous Group (Lat. creta, chalk), a series of stratified rocks forming the upper division of the secondary formation, distinguished as containing the last strata of which the fossil animal remains are wholly of extinct species. The group is subdivided into upper and lower; the former is often called from its principal member the chalk, and the latter for the same reason the greensand. The group underlies the tertiary beds of the London and Paris basins, rising up toward the straits of Dover on each side, along the coast of which its white chalk cliffs form prominent objects in the scenery. The formation is represented in New Jersey by beds of yellowish limestone and of greensand, which contain fossil shells, some of which belong to the same species, and most of them to the same genera, with those found in the cretaceous rocks of Europe. The same genera of fish also are common to the group of the two countries. The formation is traced, through the eastern part of North Carolina and central part of Georgia, and after sweeping round the southern termination of the Alleghanies in Alabama passes through that state and Mississippi northward into Tennessee and Kentucky. It is recognized near Council Bluffs on the Missouri, in Texas, in the Rocky mountains, upon the Andes near Bogota, and also in Hindostan. Thus at widely separated points in the ancient seas of four continents were similar deposits produced during the same geological period, characterized by the animal remains they include, of the same general type, and often of the same species.
For the relations of this group to those which precede and succeed it, see Geology; and for further details regarding its members, see Chalk, and Geeensand.