Cre‐ta″ceous (krē̍‐tā″shŭs), a. [L. cretaceus, fr. creta chalk. See Crayon.] Having the qualities of chalk; abounding with chalk; chalky; as, cretaceous rocks and formations. See Chalk.
Cretaceous acid, an old name for carbonic acid. — Cretaceous formation(Geol.), the series of strata of various kinds, including beds of chalk, green sand, etc., formed in the Cretaceous period; — called also the chalk formation. See the Diagram under Geology. — Cretaceous period(Geol.), the time in the latter part of the Mesozoic age during which the Cretaceous formation was deposited.