Page:Evolution of Life (Henry Cadwalader Chapman, 1873).djvu/170

same time. The earth has, no doubt, from time to time experienced great changes, its life being more or less destroyed by the effects of earthquakes, volcanoes, etc. These catastrophes were, however, local in their effects, as at the present day. If living plants and animals be compared with those whose remains have been preserved in the rocks, we see that, while many species and genera have passed away, comparatively few orders have become extinct,—that is, there are very few fossils which have not their modern representatives. Further, where the rocks overlie or follow each other, plants and animals appear in the later formation which did not pre-exist in the earlier, and usually exhibit a more complex structure. So that the "persistent types of life" seem to have been more or less modified from time to time. These general conclusions are in perfect harmony with the doctrine of the gradual development of the higher forms of life from the lower. We turn now to Embryology, which confirms, in the most remarkable way, the tree of life deduced from the structure and fossil remains of the animal and vegetal kingdoms.

CLASSIFICATION OF ROCKS ACCORDING TO THEIR ORGANIC REMAINS.

TIME.	PERIOD.		AGE.
Primary.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \ \end{matrix}}\right.}$	Silurian.	$\scriptstyle {\left\{{\begin{matrix}\ \end{matrix}}\right.}$	Mollusca, Algæ.
		Devonian	$\scriptstyle {\left\{{\begin{matrix}\ \end{matrix}}\right.}$	Fishes.
		Carboniferous.	$\scriptstyle {\left\{{\begin{matrix}\ \end{matrix}}\right.}$	Batrachia, Acrogens.
Secondary.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \ \end{matrix}}\right.}$	Triassic.	$\scriptstyle {\left.{\begin{matrix}\ \\\\\ \ \end{matrix}}\right\}\,}$	Reptiles, Cycadæ.
		Jurassic.
		Cretaceous.
Tertiary.	$\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \ \end{matrix}}\right.}$	Eocene.	$\scriptstyle {\left.{\begin{matrix}\ \\\\\ \ \end{matrix}}\right\}\,}$	Mammals, Palms, Exogens.
		Miocene.
		Pliocene.
Quaternary.	$\scriptstyle {\left\{{\begin{matrix}\ \end{matrix}}\right.}$	Modern.	$\scriptstyle {\left\{{\begin{matrix}\ \end{matrix}}\right.}$	Man.