Americans are used to thinking of our country's development as following the course of empire, i.e. East to West. But, in a larger sense, our most important avenue of development has been North-South, following the Great North Trail from Siberia, across the Bering Strait, down through Alaska, Canada, skirting the Rockies down into Mexico and even through South America. This was the path of the great migrations, both of prehistoric men and horses, and in modern times its reverse direction formed the basis for cattle drives, the Chisholm and Santa Fe trails. The Northern Rockies' trail area is ""the world's foremost bone quarry, its richest storehouse of vertebrate paleontology,"" and has yielded the bones of camels and kangaroo. And it is possible that the cradle of the human race was in Texas, not the Tigris-Euphrates valley. The study surveys buffalo trails, Indian tribes, Spanish adventures, fur traders, gold trails, cattle wars and the Klondike strike. Cushman has hardly any axes to grind and tells his story in a semi-scholarly and entertaining way.