]
In no case, however, do we ever find the Devonian resting upon
the Carboniferous, or the Silurian rocks reposing on the Devonian.
We have therefore, by a comparison of many different areas, an
established order of succession of the stratified formations, as
shown in the subjoined ideal section of the crust of the earth
(fig. 17).
The main subdivisions of the stratified rocks are known by the
following names:--
1. Laurentian.
2. Cambrian (with Huronian ?).
3. Silurian.
4. Devonian or Old Red Sandstone.
5. Carboniferous.
6. Permian \_ New Red Sandstone.
7. Triassic /
8. Jurassic or Oolitic.
9. 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). Not only do they constitute the
oldest stratified accumulations, but from the extreme divergence
between their animals and plants and those now in existence, they may
appropriately be considered as belonging to an "Old-Life" period of
the world's history. The Triassic, Jurassic, and Cretaceous systems
are grouped together as the _Secondary_ or _Mesozoic_ formations
(Gr.
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