Cretaceous

a.
  1. Having the qualities of chalk; abounding with chalk; chalky; as, cretaceous rocks and formations. See Chalk.
  2. (Geol.) Of, pertaining to, or designating, the period of time following the Jurassic and preceding the Tertiary, generally given as from 144 million years b. p. to 65 million years b. p.. Also called Cre*tac"ic.
    3. 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, and at the end of which the dinosaurs died out. See Cretaceous.