Page:Popular Science Monthly Volume 23.djvu/692

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THE POPULAR SCIENCE MONTHLY.

Rameses. The stalagmites of the Kent Cavern, England, which cover both Roman relics and palaeolithic implements of the Magdalenian period, have been made the basis of calculations which give an age of more than three hundred thousand years to the more ancient of the deposits. This, of course, is upon the supposition that the rate of incrustation has never been more rapid than it is now. Other calculations are more general in their bearing. The oscillations of the European lands under which Denmark, North Germany, and Russia have been raised from submergence during the Quaternary period, Scandinavia was depressed and has been slowly raised again, and England has been sunk till the connection that existed between it and the continent during the whole Quaternary period has been destroyed, required not less than seventy thousand years. Still another grand and surprising phenomenon, the extension of the Alpine glaciers, by which huge rocks were carried to distances of seventy or one hundred and seventy-five miles, required an enormous length of time. The maximum rate of progress of these blocks is not more than sixty metres a year; but in Quaternary times, when the slopes were not nearly so steep as now, the rate was, according to M. de Mortillet, five times slower, and each erratic block must have taken more than twenty thousand years to be carried from Mont Blanc to the lower Rhone. We may add that an enormous number of blocks were thus transported to form the terminal moraine. Add to the period of extension the period occupied in the retreat of the same glaciers, which must have been nearly as long as the other, and we shall find that the one hundred thousand years which M. de Mortillet asks for to express the duration of the glacial epoch is not an exaggeration. The epochs of the extension and retreat of the glaciers were, however, preceded by a pre-glacial period, and all the calculations together induce M. de Mortillet to adopt a total of two hundred thousand years to represent the entire duration of the Quaternary period, during which we are assured of the presence of man on European soil.

This period, long as it appears, is very short as compared with the myriads of ages of geological development that preceded it, and represents only the last and the shortest of the geological periods. The question arises, How has the human race been able to spread itself over the whole surface of the globe? Is it the product of different and independent origins in the several continents, or have all men sprung from a common cradle, a "mother-region"? On this point students are divided, Agassiz holding that men were created, and Carl Vogt that they were developed, at different centers, and Quatrefages and the theologians maintaining the unity of their origin. The fact is left that man, the same in all the essential characteristics of the species, has advanced into all the habitable parts of the globe, and that not recently, and when provided with all the resources that experience and inventive genius could put at his disposal, but when still young and