Early man did not know what time meant. He kept no records of birthdays or wedding anniversaries or the hour of death. He had no idea of days or weeks or even years. But in a general way he kept track of the seasons for he had noticed that the cold winter was invariably followed by the mild spring—that spring grew into the hot summer when fruits ripened and the wild ears of corn were ready to be eaten and that summer ended when sudden gusts of wind swept the leaves from the trees and a number of animals were getting ready for the long hibernal sleep. But now, something unusual and rather frightening had happened. Something was the matter with the weather. The warm days of summer had come very late. The fruits had not ripened. The tops of the mountains which used to be covered with grass now lay deeply hidden underneath a heavy burden of snow. Then, one morning, a number of wild people, different from the other creatures who lived in that neighbourhood, came wandering down from the region of the high peaks. They looked lean and appeared to be starving. They uttered sounds which no one could understand. They seemed to say that they were hungry. There was not food enough for both the old inhabitants and the newcomers. When they tried to stay more than a few days there was a terrible battle with claw-like hands and feet and whole families were killed. The others fled back to their mountain slopes and died in the next blizzard. But the people in the forest were greatly frightened. All the time the days grew shorter and the nights grew colder than they ought to have been. Finally, in a gap between two high hills, there appeared a tiny speck of greenish ice. Rapidly it increased in size. A gigantic glacier came sliding downhill. Huge stones were being pushed into the valley. With the noise of a dozen thunderstorms torrents of ice and mud and blocks of granite suddenly tumbled among the people of the forest and killed them while they slept. Century old trees were crushed into kindling wood. And then it began to snow. It snowed for months and months. All the plants died and the animals fled in search of the southern sun. Man hoisted his young upon his back and followed them. But he could not travel as fast as the wilder creatures and he was forced to choose between quick thinking or quick dying. He seems to have preferred the former for he has managed to survive the terrible glacial periods which upon four different occasions threatened to kill every human being on the face of the earth. In the first place it was necessary that man clothe himself lest he freeze to death. He learned how to dig holes and cover them with branches and leaves and in these traps he caught bears and hyenas, which he then killed with heavy stones and whose skins he used as coats for himself and his family.