In the British Islands, we know that the rivers had time to very materially change the surface features of the land. The important rivers of Scotland had carved out channels one hundred feet deep in places; and along their courses, especially near their mouths, had plowed out and removed great quantities of glacial material—forming broad flats which became densely wooded before Neolithic man made his appearance on the scene. In some cases the entire surface of the land had been removed, leaving only knolls and hills of the old land surface. Examples of this occur on the east coast of England, and in what is known as the Fen-lands. The final retreat of the glaciers must have left the country covered with _débris._ After this had been largely denuded, the country became densely wooded. It was not until these changes had taken place, that Neolithic man wandered into Europe.3 But still another ground exists for claiming a long interval between these two ages, namely, the great changes that took place in the animal world of Europe during these two epochs. Many different species of animals characteristic of the Paleolithic Age vanished as completely from Europe as the rude tribes that hunted them, before the appearance of Neolithic tribes. But little change in the fauna of England has taken place in the last two thousand years. So it is obvious that the great change above-mentioned demands many centuries for its accomplishment. Huge animals of the elephant kind, such as the mammoth, no longer crashed through the underbrush, or wallowed in the lakes. The roars of lions and tigers, that haunted the caves of early Europe, were no longer heard.4 In short, there had disappeared forever from Europe the distinctly southern animals that diversified the fauna of Paleolithic times. Even the Arctic animals were banished to northern latitudes, or mountain heights. We have dwelt to some length on the proofs of a long-extended time between these two ages. The more we reflect on these instances the more impressed are we with a sense of duration vast and profound, in which the great forests and grassy plains of Europe supported herds of wild animals all unvexed by the presence of man. We will only mention one more point and then pass on.