In the last chapter I had to introduce the reader to a great and terrible revolution, whereby the old Pliocene continents, with all their wealth of animals and plants, became sealed up in a mantle of Greenland ice, or, slowly sinking beneath the level of the sea, were transformed into an ocean-bottom over which icebergs bore their freight of clay and boulders. We also saw that as the Post-pliocene age advanced, the latter condition prevailed, until the waters stood more then a thousand feet deep over the plains of Europe. In this great glacial submergence, which closed the earlier Post-pliocene period, and over vast areas of the Northern Hemisphere, terminated the existence of many of the noblest forms of life, it is believed that man had no share. We have, at least as yet, no record of his presence. Out of these waters the land again rose slowly and intermittently, so that the receding waves worked even out of hard rocks ranges of coast cliff which the further elevation converted into inland terraces, and that the clay and stones deposited by the Glacial waters were in many places worked over and rearranged by the tides and waves of the shallowing sea before they were permanently raised up to undergo the action of the rains and streams, while long banks of sand and gravel were stretched across plains and the mouths of valleys, constituting "kames," or "eskers," only to be distinguished from moraines of glaciers by the stratified arrangement of their materials. Further, as the land rose, its surface was greatly and rapidly modified by rains and streams. There is the amplest evidence, both in Europe and America, that at this time the erosion by these means was enormous in comparison with anything we now experience. The rainfall must have been excessive, the volume of water in the streams very great; and the facilities for cutting channels in the old Pliocene valleys, filled to the brim with mud and boulder-clay, were unprecedented. While the area of the land was still limited, much of it would be high and broken, and it would have all the dampness of an insular climate. As it rose in height, plains which had, while under the sea, been loaded with the _débris_ swept from the land, would be raised up to experience river erosion. It was the spring-time of the Glacial era, a spring eminent for its melting snows, its rains, and its river floods.[AL] To an observer living at this time it would have seemed as if the slow process of moulding the continents was being pushed forward with unexampled rapidity. The valleys were ploughed out and cleansed, the plains levelled and overspread with beds of alluvium, giving new features of beauty and utility to the land, and preparing the way for the life of the Modern period, as if to make up for the time which had been lost in the dreary Glacial age. It will readily be understood how puzzling these deposits have been to geologists, especially to those who fail to present to their minds the