Page:Popular Science Monthly Volume 75.djvu/484

480 normally terminated. The distribution of the Pennsylvanian formations coincides with the most irregular topography of the state. The average altitude is about 770 feet, and the range in altitude is approximately 1,100 feet.

The present watershed crosses the state from east to west, trending slightly to the south, at an altitude of about 1,100 feet. Drainage lines have divided the upland portion into north-south trending blocks progressively more widely spaced towards the west. These low tracts have been used by the canals and railroads connecting Lake Erie and Ohio River.

The larger part of Ohio is an almost completely severed portion of the Allegheny plateau, extending westward from the northwestern part of Pennsylvania like a great spit into the Mississippi lowlands; the broad valley of the Ohio resembles a bay between this spit and the f western slopes of the Appalachians. This somewhat peculiar relationship of topography is the combined result of drainage adjustments due to stratigraphy, and slight diastrophic movements.

Using natural boundary lines, it would be difficult to divide North America into many states. Where such lines do exist, they have not always been utilized. Lake and river, however, form over half the border of Ohio. In general, a water boundary is an asset to a commonwealth; it may be a protection from disputes, and a transit to trade. The reaction varies with other natural boundaries: high altitudes, sometimes barriers, may impose aloofness, or almost complete isolation, whereas water boundaries invite commercial relations. Geographically Ohio is the back door of the middle and north Atlantic states. This relationship has been of reciprocal value to both areas; as population became more and more dense in the early settlements, and knowledge of the broad lands across the Appalachians spread, a movement in that direction was natural. The easiest route for the more northern of the Atlantic states was through New York via the Mohawk valley, out and along Lake Erie; for the more southern states, through passes in the mountains. Possibly on account of the narrow coastal lands to the south, or possibly because of the greater enterprise there in watching the movements of the French, the southern routes were first explored, and the earliest movements into the Ohio valley came either by way of Pittsburg or by the course of the Cumberland road.

A gross classification of the factors in the development of any region is (1) internal and (2) external. The external include the boundary itself in case the region is a natural one; but geographic situation is frequently very important. When avenues of travel and traffic converge and pass through a state benefit follows. Advantage always comes from proximity to great centers of business or culture