2. The Age of Invertebrates, represented by the Cambrian,
the Lower Silurian and the Upper Silurian rocks.
3. The Age of Fishes, represented by the Devonian rocks.
4. The Age of Amphibians, represented by the Carboniferous
rocks.
5. The Age of Reptiles, represented by the Mesozoic rocks.
6. The Age of Mammals, represented by the Cenozoic rocks.
7. The Age of Man, represented by recent rocks.
All of these Ages, which represent the life history of the world, left their impression on the rocks of their times, and each Age is connected with the preceding and the succeeding Age like links in a long, long chain.
In regard to the distinctness and importance of the last great era, the Age of Man, Le Conte, in "Elements of Geology," says that there are two views which will ever divide geologists, depending on the two views regarding the relation of man to Nature:
"From a purely structural and animal point of view, man is very closely united with the animal kingdom. He has no department of his own, but belongs to the vertebrate department, along with the quadrupeds, birds, reptiles and fishes. He has no class of his own, but belongs to the class Mammalia, along with the quadrupeds. Neither has he an order of his own, but belongs to the order of the Primates, along with the monkeys, lemurs, etc. Even a family of his own, the Hominidae, is grudgingly admitted by some. But from a psychical point of view it is simply impossible to overestimate the space which separates man from all lower things. Man must be set off not only against the whole animal kingdom, but against the whole book of Nature besides, as an equivalent: Nature the Book—the revelation—and man the interpreter. So in the history of the earth: from one point of view the era of man is not equivalent to an era, nor to an age, nor to a period, nor even to an epoch. But from another point of view it is the equivalent of the whole geological history of the earth besides. For the history of the earth finds its consummation, and its interpreter, and its significance, in man."
Ah—how exhilarating the thought! Once again with the astronomer, we gaze out on the huge planets of the solar system,—the groups and great galaxies of stars. Does the earth really seem so insignificant in its smallness?