How long our continental plateaus remained under the icy seas of the Glacial period we do not know. Relatively to human chronology, it was no doubt a long time; but short in comparison with those older subsidences in which the great Palæozoic limestones were produced. At length, however, the change came. Slowly and gradually, or by intermittent lifts, the land rose: and as it did so, shallow-water sands and gravels were deposited on the surface of the deep-sea clays, and the sides of the hills were cut into inland cliffs and terraces, marking the stages of recession of the waters. At length, when the process was complete, our present continents stood forth in their existing proportions ready for the occupancy of man.
The picture which these changes present to the imagination is one of the most extraordinary in all geological history. We have been familiar with the idea of worlds drowned in water, and the primeval incandescent earth shows us the possibility of our globe being melted with fervent heat; but here we have a world apparently frozen out destroyed by cold, or doubly destroyed by ice and water. Let us endeavour to realise this revolution, as it may have occurred in any of the temperate regions of the Northern Hemisphere, thickly peopled with the magnificent animals that had come down from the grand old Miocene time. Gradually the warm and equable temperature gives place to cold winters and chilly wet summers. The more tender animals die out, and the less hardy plants begin to be winter-killed, or to fail to perfect their fruits. As the forests are thus decimated, other and hardier species replace those which disappear. The animals which have had to confine themselves to sheltered spots, or which have perished through cold or want of food, are replaced by others migrating from the mountains, or from colder regions. Some, perhaps, in the course of generations, become dwarfed in stature, and covered with more shaggy fur. Permanent snow at length appears upon the hill-tops, and glaciers plough their way downward, devastating the forests, encroaching on the fertile plains, and at length reaching the heads of the bays and fiords. While snow and ice are thus encroaching from above, the land is subsiding, and the sea is advancing upon it, while great icebergs drifting on the coasts still further reduce the temperature. Torrents and avalanches from the hills carry mud and gravel over the plains. Peat bogs accumulate in the hollows. Glaciers heap up confused masses of moraine, and the advancing sea piles up stones and shingle to be imbedded in mud on its further advance, while boreal marine animals invade the now submerged plains. At length the ice and water meet everywhere, or leave only a few green strips where hardy Arctic plants still survive, and a few well-clad animals manage to protract their existence. Perhaps even these are overwhelmed, and the curtain of the Glacial winter falls over the fair scenery of the Pliocene. In every locality thus invaded by an apparently perpetual winter, some species of laud animals must have perished. Others may have migrated to more genial climes, others under depauperated and hardy varietal forms may have continued successfully to struggle for existence. The general result must have been greatly to diminish the nobler forms of life, and to encourage only those fitted for the most rigorous climates and least productive soils.
Could we have visited the world in this dreary period, and have witnessed the decadence and death of that brilliant and magnificent flora and fauna which we have traced upward from the Eocene, we might well have despaired of the earth’s destinies, and have fancied it the sport of some malignant demon; or have supposed that in the contest between the powers of destruction and those of renovation the former had finally gained the victory. We must observe, however, that the suffering in such a process is less than we might suppose. So long as animals could exist, they would continue to enjoy life. The conditions unfavourable to them would be equally or more so to their natural enemies. Only the last survivors would meet with what might be regarded as a tragical end. As one description of animal became extinct, another was prepared to occupy its room. If elephants and rhinoceroses perished from the land, countless herds of walruses and seals took their places. If gay insects died and disappeared, shell-fishes and sea-stars were their successors.
Thus in nature there is life even in death, and constant enjoyment even when old systems are passing away. But could we have survived the Glacial period, we should have seen a reason for its apparently wholesale destruction. Out of that chaos came at length an Eden; and just as the Permian prepared the way for the Mesozoic, so the glaciers and icebergs of the Post-pliocene were the ploughshare of God preparing the earth for the time when, with a flora and fauna more beautiful and useful, if less magnificent than that of the Tertiary, it became as the garden of the Lord, fitted for the reception of His image and likeness, immortal and intelligent Man. We need not, however, with one modern school of philosophy, regard man himself as but a descendant of Miocene apes, scourged into reason and humanity by the struggle for existence in the Glacial period. We may be content to consider him as a son of God, and to study in the succeeding chapters that renewal of the Post-pliocene world which preceded and heralded his advent.
In the meantime, our illustration,[AK] borrowed in part from the magnificent representation of the Post-pliocene fauna of England, by the great restorer of extinct animals, Mr. Waterhouse Hawkins, may serve to give some idea of the grand and massive forms of animal life which, even in the higher latitudes, survived the Post-pliocene cold, and only decayed and disappeared under that amelioration of physical conditions which marks the introduction of the human period.
[AK] Page 301.
CLOSE OF THE POST-PLIOCENE, AND ADVENT OF MAN.