A RIVER FLOOD-PLAIN—A REGION ADAPTED TO CULTIVATION
The result of these conditions is evident. The Atlantic slopes, though not everywhere the most densely peopled areas, contain the great centres of the world's activities and economies. In the past 400 years they have not only overtaken the Pacific coast races, but have far surpassed them. They are now entering upon a commercial invasion of the Pacific nations that is resulting in a reorganization of the entire industrial world.
Topography and Trade Routes.—As the settlement and commerce of a country grow, roads succeed trails, and trails are apt to follow the paths of migrating animals. Until the time of the Civil War in the United States, most of the great highways of the country were the direct descendants of "buffalo roads," as they were formerly called.
In the crossing of divides from one river-valley to another, the mountain-sections of the railways for the greater part follow the trails of the bison. This is especially marked in the Pennsylvania, the Baltimore and Ohio, and the Chesapeake and Ohio railways; in some instances the tunnels through ranges have been constructed directly under the trails. The reason is obvious; the instinct of the bison led him along routes having the minimum of grade.
Throughout the Mississippi Valley and the great plains the Indian trails usually avoided the bottom-lands of the river-valleys, following the divides and portages instead. This selection of routes was probably due to the fact that the lowlands were swampy and subject to overflow; the portages and divides offered no steep grades, and were therefore more easily traversed.
