The most illuminating accomplishment of the table, however, is its bird's-eye view of the procession of the evolution of life from the first inference of its existence to its climax of to-day; and, concurrent with this progress, its suggestion of the growth and development of scenic America. It is, in effect, the table of contents of a volume whose thrilling text and stupendous illustration are engraved immortally in the rocks; a volume whose ultimate secrets the scholarship of all time perhaps will never fully decipher, but whose dramatic outlines and many of whose most thrilling incidents are open to all at the expense of a little study at home and a little thoughtful seeing in the places where the facts are pictured in lines so big and graphic that none may miss their meanings.

Man's colossal egotism is rudely shaken before the Procession of the Ages. Aghast, he discovers that the billions of years which have wrought this earth from star dust were not merely God's laborious preparation of a habitation fit for so admirable an occupant; that man, on the contrary, is nothing more or less than the present master tenant of earth, the highest type of hundreds of millions of years of succeeding tenants only because he is the latest in evolution.

PROGRESS OF CREATION

Chart of the Divisions of Geologic Time, and an Estimate in Years based on the assumption that a hundred million years have elapsed since the close of the Archean Period, together with a condensed table of the Evolution of Life from its Inferred Beginnings in the Archean to the Present Time. Read from the bottom up. Read the footnote upon the opposite page concerning the Estimate of Time.

ERAPERIODEPOCHLIFE DEVELOPMENTESTIMATED
TIME
Cenozoic
Era of
Recent
Life		QuaternaryRecent
Pleistocene
(Ice Age)

The Age of Man

Animals and plants of the modern type. First record of man occurs in the early Pleistocene.		6
millions
of
years.
TertiaryPliocene
Miocene
Oligocene
Eocene

The Age of Mammals

Rise and development of the highest orders of plants and animals.
Mesozoic
Era of
Intermediate
Life		Cretaceous

The Age of Reptiles

Shellfish with complex shells. Enormous land reptiles. Flying reptiles and the evolution therefrom of birds. First palms. First hardwood trees. First mammals.		16
millions
of
years.
Jurassic
Triassic
CarboniferousPermian
Pennsylvanian
Mississippian

The Age of Amphibians. The Coal Age

Sharks and sea animals with nautilus-like shells. Evolution of land plants in many complex forms. First appearance of land vertebrates. First flowering plants. First cone-bearing trees. Club mosses and ferns highly developed.
Paleozoic
Era of
Old Life		Devonian

The Age of Fishes

Evolution of many forms. Fish of great size. First appearance of amphibians and land plants.		45
millions
of years.
Silurian Shellfish develop fully. Appearance and culmination of crinoids or sea-lilies, and large scorpion-like crustaceans. First appearance of reef-building corals. Development of fishes.
Ordovician Sea animals develop shells, especially cephalopods and mollusk-like brachiopods. Trilobites at their height. First appearance of insects. First appearance of fishes.
Cambrian More highly developed forms of water life. Trilobites and brachiopods most abundant. Algæ.
ProterozoicAlgonkian The first life which left a distinct record. Very primitive forms of water life, crustaceans, brachiopods and algæ. 33 millions
of years.
ArcheozoicArchean No fossils found, but life inferred from the existence of iron ores and limestones, which are generally formed in the presence of organisms.

Who can safely declare that the day will not come when a new Yellowstone, hurled from reopened volcanoes, shall found itself upon the buried ruin of the present Yellowstone; when the present Sierra shall have disappeared into the Pacific and the deserts of the Great Basin become the gardens of the hemisphere; when a new Rocky Mountain system shall have grown upon the eroded and dissipated granites of the present; when shallow seas shall join anew Hudson Bay with the Gulf of Mexico; when a new and lofty Appalachian Range shall replace the rounded summits of to-day; when a race of beings as superior to man, intellectually and spiritually, as man is superior to the ape, shall endeavor to reconstruct a picture of man from the occasional remnants which floods may wash into view?

NOTE EXPLANATORY OF THE ESTIMATE OF GEOLOGIC TIME IN THE TABLE ON THE OPPOSITE PAGE

The general assumption of modern geologists is that a hundred million years have elapsed since the close of the Archean period; at least this is a round number, convenient for thinking and discussion. The recent tendency has been greatly to increase conceptions of geologic time over the highly conservative estimates of a few years ago, and a strong disposition is shown to regard the Algonkian period as one of very great length, extremists even suggesting that it may have equalled all time since. For the purposes of this popular book, then, let us conceive that the earth has existed for a hundred million years since Archean times, and that one-third of this was Algonkian; and let us apportion the two-thirds remaining among succeeding eras in the average of the proportions adopted by Professor Joseph Barrell of Yale University, whose recent speculations upon geologic time have attracted wide attention.