Page:Popular Science Monthly Volume 10.djvu/606

588 that man could not have originated at the foot of the glacier. The ice must have met him toward the close of the Tertiary period in the northern parts of Asia and America, and forced him southward; or, at a later time, it must have found him on the main belt of this continent. The Tertiary origin of man is presupposed, from the fact that he had submitted to a race-modification fitting him to endure the cold.

Let us consider for a moment what this glacial epoch really was. As to its occurrence, the ice has left its mark on the rocks, and we see its moraines and transported bowlders over a vast portion of this continent from Virginia to the Pacific. There is no doubt that a vast ice-sheet, a continental system of glaciers, was here at a distant time. It has transported masses of rock, and left them on the summit of Mount Washington, where they still remain, and to do this it must at one time have overtopped the mountain. The ice gradually spread from the north, and its progress was slow, as we judge of time—so slow that it must have seemed immovable and unchanging from year to year, to the man of the epoch, just as it seems to us now; and just as slowly as it advanced it retired again to where it is to-day.

The glacial epoch comes in between the present or Quaternary division of time and the Tertiary. In order to estimate its effects, we must briefly consider the aspect of the earth before its advent and in the preceding epochs.

There are two principal conclusions to be drawn from an examination of the fossil remains of plants and animals during the Tertiary. The first is, that the climate over the largest portion of the globe was then equable. There were then apparently no seasons—the summer seems to have been perpetual. The proof of this lies in the fact that there was a general distribution of plants and animals over the whole surface. In Greenland and Arctic America there were forests of trees, as attested by the remains of their trunks, stumps, and leaves. The same regions reveal to us coal-fields, and the fossil remains of reptiles like those we find in beds of the now temperate zone. We find beds of coal on desolate islands in the Southern Pacific Ocean, islands so cold and barren as to afford now but weak and little plants; whereas these beds of coal attest the presence once of a luxurious vegetation, of which they are the remains.

The second conclusion is, that the Tertiary was the richest in the number and kinds of the higher animals as compared with the present or any preceding geological period in the earth's history. Then our Territories supported all the various kinds of animals, for instance, which culminated in the horse. The remains of hundreds of species of animals have been collected by Prof. Marsh from a region which now supports but very few.

Prof. Huxley has, by his now famous lectures in New York City the past year, made popularly known the discoveries of fossils by