regions where people dwell in greatest numbers. The plains in the
two great land masses of the Old World and the New have the same
inverse or right- and left-handed symmetry as the mountains. In
the north the vast stretches from the Mackenzie River to the Gulf
of Mexico correspond to the plains of Siberia and Russia from the
Lena to the Black Sea. Both regions have a vast sweep of
monotonous tundras at the north and both become fertile granaries
in the center. Before the white man introduced the horse, the ox,
and iron ploughs, there prevailed an extraordinary similarity in
the habits of the plains Indians from Texas to Alberta. All alike
depended on the buffalo; all hunted him in much the same way; all
used his skins for tents and robes, his bones for tools, and his
horns for utensils. All alike made him the center of their
elaborate rituals and dances. Because the plains of North America
were easy to traverse, the relatively high culture of the ancient
people of the South spread into the Mississippi Valley. Hence the
Natchez tribe of Mississippi had a highly developed form of
sun-worship and a well-defined caste system with three grades of
nobility in addition to the common people. Even farther north,
almost to the Ohio River, traces of the sun-worship of Mexico had
penetrated along the easy pathway of the plains.

South of the great granaries of North America and Eurasia the
plains are broken, but occur again in the Orinoco region of South
America and the Sahara of Africa. Thence they stretch almost
unbroken toward the southern end of the continents. In view of
the fertility of the plains it is strange that the centers of
civilization have so rarely been formed in these vast level
expanses.