When the sun arose in the morning he did not say "Behold another day."
He said "It is Light" and he used the rays of the early sun to gather
food for his family.

When it grew dark, he returned to his wife and children, gave them part
of the day's catch (some berries and a few birds), stuffed himself full
with raw meat and went to sleep.

In a very general way he kept track of the seasons. Long experience had
taught him 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 plucked and eaten. The Summer ended
when gusts of wind swept the leaves from the trees and when a number of
animals crept into their holes to make ready for the long
hibernal sleep.

[Illustration: THE GLACIAL PERIOD.]

It had always been that way. Early man accepted these useful changes of
cold and warm but asked no questions. He lived and that was enough to
satisfy him.

Suddenly, however, something happened that worried him greatly.

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