CHAPTER II.
GLACIAL EPOCH.
Happily for the Archæo-geologist, there is given him a point from which to start in his researches into the antiquity of his race. Without it his calculations would be very indefinite and his efforts would be shorn of much of their interest. The Glacial Epoch, that has puzzled the mind of both the geologist and the astronomer, is a guide-post where he may not only look both ways, but also estimate the length of ages and number the years of man. Nothing, then, is of more importance, in this investigation, than an understanding of the condition of the earth prior to the glacial, and the knowledge of the date and length of this epoch.
For untold ages the earth, to all appearance, had been preparing itself for the reception of man. There was an abundance of game, the forests were beautiful, the domestic animals had made their appearance, the climate was warm, the soil rich, and the coal had been formed. Everything seemed to point to a bright and glorious future for man, who had already entered upon the scene. It is true there were fierce and savage beasts to contend with. These seemed but a motive power to stir man to action and develop the resources of his mind. Should he fail for a time to overcome the wild beasts a retreat was provided in the hollow recesses of the earth. But nature felt her work was still unfinished. The earth had passed through the ordeal of fire, and withstood the devastations of water, and now her long summer must come to an end. The arctic regions had been growing colder and colder, and the change was felt in the countries to the south. The northern animals were being clothed with a hairy or woolly garment for their protection. The aspect began to be forbidding. The future prospect of man was not only gloomy, but foreboded he should perish along with the many species of animals that were gradually succumbing to the cold. Great fields of ice were slowly accumulating at both the poles, and at last, by the power of their great weight, assisted by some geographical changes, began to move toward the equator, crushing and grinding the great rocks, and either driving before them, or else destroying, every living thing in their relentless march. Slowly but surely they moved on. The mountains groaned under the enormous weight of ice. Their heads were scarred, their sides bruised, torn and cut. The icy monsters listened not to the pleadings of earth, the lowing of cattle, or the cries of man. Centuries elapsed before the sun re-asserted his power. The rays of the sun, the internal heat of the earth, and other causes, produced a change. The northern ice was broken up by the time it reached latitude 39° North America, leaving its indelible traces in the bowlders, gravel, beds of sand and clay which mark its course. In Europe this sheet of ice extended as far south as Spain and Corsica. The glaciers of the Antarctic regions extended as far as latitude 41° south.
Fauna of Europe.—Among the Fauna may be mentioned the gigantic elephants, of nearly twice the bulk of the largest individuals that now exist, which roamed in herds over England, and extended across the Siberian plains and from Behring Strait to South Carolina. Two-horned rhinoceroses wallowed in the swamps of the ancient forests. Hippopotamuses inhabited the lakes and rivers. The great cave-bear, which sometimes attained the size of a horse, and the cave-tiger, twice as large as the living tiger, preyed upon the animals of less strength than themselves. Troops of hyenas, larger than those of South America, disputed with other beasts of prey. A species of wild-cat, lynx, and leopard found retreats in the same forests. Then there was a remarkable carnivorous animal called Machairodus, about the size of a tiger, and from the shape and size of the sword-like teeth, must have been a very destructive creature. The lemming and the musk ox found a home, and the wild horse pranced about unrestrained by the hand of man. The great Irish elks swiftly moved over the ground, and must have been very numerous, as their remains occur in abundance in peat-bogs and marl-pits. Nor should it be unmentioned that there was also a species of gigantic ox nearly as large as an elephant, that subsisted on the plains. All these animals followed the retreat of the glaciers and some of them were in close proximity to the ice.
Geological Period.—The glacial epoch occurred during the geological period known as the post-tertiary. The tertiary had gradually passed away and its time had been recorded on the pages of geological history. A new epoch began to dawn. This was the epoch of ice, the birth and almost the childhood of the post-tertiary.
Probable Date.—In discussing the probable date of the glacial epoch, Sir Charles Lyell says, "The attempt to assign a chronological value to any of our geological periods except the latest, must, in the present state of science, be hopeless. Nevertheless, independently of all astronomical considerations, it must, I think, be conceded that the period required for the coming on of the greatest cold, and for its duration when most intense, and the oscillations to which it was subject, as well as the retreat of the glaciers and the 'great thaw' or disappearance of snow from many mountain-chains where the snow was once perpetual, required not tens but hundreds of thousands of years. Less time would not suffice for the changes in physical geography and organic life of which we have evidence. To a geologist, therefore, it would not appear startling that the greatest cold should be supposed to have been two hundred thousand years ago, although this date must be considered as very conjectural, and one which may be as likely to err in deficiency of time as in excess."[6]
Sir John Lubbock, in his dissent from some calculations made by Mr. Geikie on the general effect produced by rivers in excavating valleys and lowering the general level of the country, says, "As regards the higher districts, however, his data are perhaps not far wrong, and if we apply them to the valley of the Somme, where the excavation is about two hundred feet in depth, they would indicate an antiquity for the palæolithic epoch of from one hundred thousand to two hundred and forty thousand years."[7]