The Probert Encyclopaedia of Rocks & Minerals

CRETACEOUS

The Cretaceous was the eleventh geological period, 95,000,000 years ago, following the Jurassic and preceding the Eocene. The first marsupials evolved during this period. The cretaceous forms the upper strata of the Secondary series, immediately below the Tertiary series, and superincumbent on the Oolite system. This group is common to Europe, and also to a part of Asia. It consists of chalk resting upon arenaceous and argillaceous deposits, which are also regarded as part of the system. It has been divided into two parts: the Upper, consisting entirely of chalk or marl, and subdivided into the upper or soft chalk, containing many flint and chert nodules; the lower or harder chalk, with fewer flints; and the chalk marl: and the Lower, consisting of sands and clay, and subdivided into the upper greensand; gault, a bluish tenacious clay; and the lower greensand. Palaeontologists have suggested another division founded on the fossil remains found in the system, in accordance with which the upper greensand and gault are transferred to the upper series, and the lower greensand and Wealden beds and Hastings sands constitute the lower.
Research Cretaceous