The topographic and climatic features of these various regions have had a great influence not only on the political history of the country, but their effect has been even greater in determining its industrial development. They have resulted in the establishment of the various industries, each in the locality best adapted to it, instead of their diffusion without respect to the necessary conditions of environment. The foregoing regions are also approximately areas of fundamental industries. Thus, the New England plateau supplies the rest of the United States with light manufactures, such as cotton textiles, woollen clothing, hats, shoes, cutlery, books, writing-paper, household metal wares, etc., but sells the excess abroad. The middle and southern Appalachians, with the coal which forms their chief resource, supply the rest of the country with structural steel, from ores obtained in the lake regions, and sell the excess to foreign countries. The northern Mississippi Valley grows nearly one-fourth of the world's wheat-crop. The wheat of this region and the Pacific coast lowlands supplies the country with bread-stuffs, and exports the excess to western Europe. The Gulf states, which produce three-fourths of the world's cotton-crop, supply the whole country and about one-half the rest of the world besides with cotton textiles. The grazing regions produce an excess of meat for export; the western highlands furnish the gold and silver necessary to carry on the enormous commerce. In the last twenty years the imports of merchandise per capita varied but little from $11.50; the exports per capita varied from about $12 to more than $18. =The Atlantic Coast-Plain and the Seaports.=--Throughout most of its extent the Atlantic seaboard of the United States is bordered by a low coast-plain. Along the northeastern coast of the United States the coast-plain is very narrow; south of New York Bay it has a width in some places of more than two hundred miles. The existence of this plain has had a marked effect on the commercial development of the country. The sinking or "drowning" of the northern part of it has made an exceedingly indented coast. The drowned valleys, enclosed by ridges and headlands, form the best of harbors, and nearly all of them are northeast of New York Bay. South of New York Bay good harbors are comparatively few. For the greater part they occur only when old, buried river-channels permit approach to the shore.