Except on their southern borders the great northern forests are not good as a permanent home for man.

Thus the races, though alike in their physical response to climate, may possibly be different in their mental response because they have approached America by different paths.

Although mountains may guide migrations, the plains are the regions where people dwell in greatest numbers.

The whole history of life is a record of cycles.

Although farming of any sort was almost as impossible in the plains as in the dry regions of winter rains farther west, the abundance of buffaloes made life much easier in many respects.

No part of the world can be truly understood without a knowledge of its garment of vegetation, for this determines not only the nature of the animal inhabitants but also the occupations of the majority of human beings.

In fact, the history of North America has been perhaps more profoundly influenced by man's inheritance from his past homes than by the physical features of his present home.