IN the preceding chapters I have endeavoured to show that the study of the successive phases of the glacial period in Europe, and the enduring marks which they have left on many of the solid rocks and on the character of the superficial drift, are of great assistance in enabling us to appreciate the vast lapse of ages which are comprised in the postpliocene epoch. They enlarge at the same time our conception of the antiquity, not only of the living species of animals and plants, but of their present geographical distribution, and throw light on the chronological relations of these species to the earliest date yet ascertained for the existence of the human race. That date, it will be seen, is very remote if compared to the times of history and tradition, yet very modern if contrasted with the length of time during which all the living testacea, and even many of the mammalia, have inhabited the globe.

In order to render my account of the phenomena of the glacial epoch more complete, I shall describe in this chapter some other changes in physical geography, and in the internal structure of the earth's crust, which have happened in the post-pliocene period, because they differ in kind from any previously alluded to, and are of a class which were thought by the earlier geologists to belong exclusively to epochs anterior to the origin of the existing fauna and flora.