Of such changes, not the greatest, but the most interesting to the question we have at present in hand, were those vicissitudes of climate which followed upon the time when the formation of the crust of the earth had been practically completed. We learn of a time when, instead of the temperate climate which now favours our country, these islands, with the whole of the north of Europe, were wrapped in one impenetrable sheet of ice. The tops of our mountains, as well as of those of Scandinavia and the north of continental Europe, bear marks of the scraping of this enormous glacier, which must have risen to a height of two or three thousand feet. Not a single green thing, therefore, might be seen between our latitudes and the pole, while the ice-sheet, passing along the floor of the North Sea, united these islands with Scandinavia and spread far out into the deep waters of the Atlantic. For thousands of years such a state of things endured, but at last it slowly passed away. As century followed century the glacier began to decrease in size. From being colder than that of any explored portion of our hemisphere, the climate of northern Europe began to amend, until at last a little land became visible, which was covered first with lichens, then with thicker moss, and then with grass; then shrubs began to grow, and they expanded into trees and the trees into forests, while still the ice-sheet went on decreasing, until now the glaciers remained only in the hills. Animals returned from warmer climates to visit our shores. The birds and beasts and fishes of the land and sea were not much different from those which now inhabit there; the species were different, but the genera were for the most part the same. Everything seemed to have been preparing for the coming of man, and it is about this time that we find the earliest traces of his presence upon earth.[2]
We may try and imagine what was the appearance of the world, and especially of Europe--for it is in Europe that most of these earliest traces of our race have as yet been found, though all tradition and likelihood point out man’s first home to have been in Asia--when we suppose that man first appeared upon these western shores. At this time the continent of Europe stood at a higher level than it does now. The whole of the North Sea, even between Scotland and Denmark, is not more than fifty fathoms, or three hundred feet deep, while the Irish Sea is not more than sixty fathoms; and at this period undoubtedly the British Isles, besides being all joined together, formed part of the mainland, not by being united to France only, but by the presence of dry land all the way from Scotland to Denmark, over all that area now called the German Ocean. Our Thames and our other eastern rivers were then but tributaries of one large stream, which bore through this continent, and up into the northern seas, their waters united with those of the Rhine, and perhaps of the Weser and the Elbe. The same upheaval turned into land a portion of the Atlantic Ocean, all that bed probably which now extends from Spain and Africa as far as the Azores and the Canaries. The north of Africa was joined on to this continent and to Spain, for the narrow Straits of Gibraltar had not yet been formed; but a great sea stood where we now have the Great Sahara, and united the Mediterranean and the Red Sea, while a great Mediterranean Sea stood in Central Asia, and has left no more than traces in the Caspian Sea and the Sea of Aral.