Geologists are rapidly becoming convinced that the mammals spread from their central Asian point of origin largely because of great variations in climate.

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.

Year by year we are learning that in this restless, strenuous American life of ours vacations are essential.

Fertile soil, level plains, easy passage across the mountains, coal, iron, and other metals imbedded in the rocks, and a stimulating climate, all shower their blessings upon man.

From first to last the civilization of America has been bound up with its physical environment.

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

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.