Читать книгу The Book of the National Parks - Robert Sterling Yard - Страница 8

From a photograph by Bailey Willis

MIDDLE FORK OF THE BELLY RIVER, GLACIER NATIONAL PARK

Very ancient shales and limestone fantastically carved by glaciers. The illustration shows Glenns Lake, Pyramid Peak, Chaney Glacier, and Mount Kipp

Years mean nothing in the computation of the prehistoric past. Who can conceive a thousand centuries, to say nothing of a million years? Yet either is inconsiderable against the total lapse of time even from the Archean's close till now.

And so geologists have devised an easier method of count, measured not by units of time, but by what each phase of progress has accomplished. This measure is set forth in the accompanying table, together with a conjecture concerning the lapse of time in terms of years.

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.

ERA	PERIOD	EPOCH	LIFE DEVELOPMENT	ESTIMATED TIME
Cenozoic Era of Recent Life	Quaternary	Recent Pleistocene (Ice Age)	The Age of ManAnimals and plants of the modern type. First record of man occurs in the early Pleistocene.	6 millions of years.
Tertiary	Pliocene Miocene Oligocene Eocene	The Age of MammalsRise and development of the highest orders of plants and animals.
Mesozoic Era of Intermediate Life	Cretaceous		The Age of ReptilesShellfish 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
Carboniferous	Permian Pennsylvanian Mississippian	The Age of Amphibians. The Coal AgeSharks 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 FishesEvolution 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.
Proterozoic	Algonkian		The first life which left a distinct record. Very primitive forms of water life, crustaceans, brachiopods and algæ.	33 millions of years.
Archeozoic	Archean		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.

Fantastic, you may say. It is fantastic. So far as I know there exists not one fact upon which definite predictions such as these may be based. But also there exists not one fact which warrants specific denial of predictions such as these. And if any inference whatever may be made from earth's history it is the inevitable inference that the period in which man lives is merely one step in an evolution of matter, mind and spirit which looks forward to changes as mighty or mightier than those I have suggested.

With so inspiring an outline, the study to which I invite you can be nothing but pleasurable. Space does not permit the development of the theme in the pages which follow, but the book will have failed if it does not, incidental to its main purposes, entangle the reader in the charm of America's adventurous past.