The mode of life, together with the trials of his strength, developed his muscular system. His muscles became large and tough, and his bones thick and heavy. The earliest type of man is generally supposed to be _dolichocephalic_, or long-headed. The walls of the skull were thick, and the crown low. He was of ordinary stature, but built for action, and of great power. His make-up was the result of his surroundings. His advancement was very slow. Throughout the entire length of the miocene and pliocene epochs it is not traceable. There was no revolution in his mind; one step in advance would have been a mighty leap. Nor could it be expected that there should be rapid progress. The mind was brutal; and all the instincts sensual. But there was pending a mighty change. The tropical climate should change into a winter of snow and ice. Man should feel it, and be benefited by the new danger. His sluggish mind should be quickened, and the inventive genius should be called into action. The sun no longer could give its heat. The forests grew cold, the chilling winds swept over the plains, and the retreat in the cave was damp and forbidding. The wild beasts were either dying of cold, or else becoming clothed with thick, long hair, and retreating before the accumulating snow. Man earnestly looked about him. He suffered greatly, and his numbers grew less. Fire had been produced. How, no one can tell; possibly by accident. He now became more careful of the fire, and with brand in hand he went from place to place kindling the fires at the various resting-places. Nor was this sufficient. His ingenuity was taxed to its greatest extent. Colder and colder grew the winds. The snow, coming in great flakes, was soon consolidated, and became as ice. The body could not be kept warm. Clothing must be had, and this must be furnished by the wild beasts. Their hides must assist in protecting the life of man. The stiffened, frozen animals would not alone furnish sufficient covering. Knives must be invented. From the flint rude knives were fashioned, by means of which the skins were removed and transferred to the bodies of men. But the long winter continuing, the lives of the living animals must be forfeited, both for the flesh and and the skins. Rude, almost shapeless arrow-heads were produced. Wood must be had with which to warm and cook, and rude rafts formed, by means of which the swelling rivers might be crossed. Then those stone hatchets of the Somme were shaped, and answered the purpose.