The warm days of Summer had come very late. The fruits had not ripened at all. The tops of the mountains which used to be covered with grass lay deeply hidden under a heavy burden of snow. Then one morning quite a number of wild people, different from the other inhabitants of his valley had approached from the region of the high peaks. They muttered sounds which no one could understand. They looked lean and appeared to be starving. Hunger and cold seemed to have driven them from their former homes. There was not enough food in the valley for both the old inhabitants and the newcomers. When they tried to stay more than a few days there was a terrible fight and whole families were killed. The others fled into the woods and were not seen again. For a long time nothing occurred of any importance. But all the while, the days grew shorter and the nights were colder than they ought to have been. Finally, in a gap between the two high hills, there appeared a tiny speck of greenish ice. It increased in size as the years went by. Very slowly a gigantic glacier was sliding down the slopes of the mountain ridge. Huge stones were being pushed into the valley. With the noise of a dozen thunderstorms they suddenly tumbled among the frightened people and killed them while they slept. Century-old trees were crushed into kindling wood by the high walls of ice that knew of no mercy to either man or beast. At last, it began to snow. It snowed for months and months and months. [Illustration: THE CAVE-MAN.] All the plants died. The animals fled in search of the southern sun. The valley became uninhabitable. Man hoisted his children upon his back, took the few pieces of stone which he had used as a weapon and went forth to find a new home. Why the world should have grown cold at that particular moment, we do not know. We can not even guess at the cause. The gradual lowering of the temperature, however, made a great difference to the human race. For a time it looked as if every one would die. But in the end this period of suffering proved a real blessing. It killed all the weaker people and forced the survivors to sharpen their wits lest they perish, too. Placed before the choice of hard thinking or quick dying the same brain that had first turned a stone into a hatchet now solved difficulties which had never faced the older generations. In the first place, there was the question of clothing. It had grown much too cold to do without some sort of artificial covering. Bears and bisons and other animals who live in northern regions are protected against snow and ice by a heavy coat of fur. Man possessed no such coat. His skin was very delicate and he suffered greatly.