Cretaceous.
10.

Eocene.
11.

Miocene.
12.

Pliocene.
13.

Post-tertiary.
[Illustration: Fig.17.IDEAL SECTION OF THE CRUST OF THE EARTH.] Of these primary rock divisions, the Laurentian, Cambrian, Silurian, Devonian, Carboniferous, and Permian are collectively grouped together under the name of the Primary or _Paloeozoic_ rocks (Gr.
_palaios_, ancient; _zoe_, life).