What does "cretaceous" mean?

Cretaceous: 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.