The Cretaceous time period lasted from 146 to 65 million
years ago, a time span of 81 million years. The Cretaceous Period is the
last of the Mesozoic Era. The term Cretaceous was first used in the 1820s
to describe the "Terrain Cretace," the chalk deposits of the Paris Basin
and the English Channel. These Cretaceous rocks were defined based on
a particular type of fossil assemblage contained within them. They are
located above the rocks of the Jurassic System
and below the rocks of the Tertiary System.