cretaceous adj.

1670s, "chalky," from Latin cretaceus "chalk-like," from creta "chalk." As a geological period (with a capital C-) between the Jurassic and the Tertiary, it is attested from 1851, a reference to the extensive chalk beds of southeastern England that were laid down during the Cretaceous and studied in the early years of geology. In reference to the chalk beds, cretaceous is attested in geology writing by 1832.