THE UNITED STATES.—The New England States, which belong to the northern part of the Appalachian system, form a natural region. They consist of a glaciated peneplain from which much of the soil has been removed, and over which great glacial blocks render cultivation difficult. They are isolated from the remainder of the continent, and communication with the interior is greatly impeded. The inhabitants eventually found agriculture unprofit able, and turned to manufactures, finding a source of power in the waters descending glacial-dammed valleys.
The Middle Appalachian States, with the corresponding part of the coastal plain, really form a unit despite differences in topo graphy, climate, and products. Their position with regard to the ocean and the interior, their communications, and above all their great coal supplies, knit them together and make them the great manufacturing region of the United States.
The Southern Appalachians differ in structure in some respects from the Northern. They possess both coal and iron, and their position in relation to the great cotton-growing region of the United States is leading to a distinct type of economic development.
To the west of the northern part of the Appalachians is the glaciated area of the central plains. The Laurentian ice-sheet made its way southwards during glacial times, entered what is now the United States, and covered all the area east of the Missouri and north of a line drawn from Nashville, by way of Philadelphia, to New York. Over the central plains the till deposited by the ice sheet generally forms a fertile soil, the land is flat, and, outside of the forested area easily cultivated ; the climate, cold in winter, is warm in summer, and the rainfall is sufficient for the growth of wheat and maize. All these conditions mark this area out as the great agricultural region of the United States. Along with it may be included the remainder of the prairie region north of the Ozark uplift.
The Atlantic and Gulf Coastal Plains, along with which that part of the prairie belt south of the Ozark uplift may be included for the sake of convenience, are destined by climatic conditions to be the great cotton-producing region of the United States. Their
economic development differs in many respects from other parts of the country, and these differences are primarily due to the nature of the geographic control.
The Great Plateaus are marked out by physical features, climate, and vegetation as one large natural region. Their undulating surface, considerable elevation, dry climate, and xerophilous vegetation combine to distinguish them from the regions further to the east. Within so great an area there are naturally considerable differences, but with certain exceptions, to be noted later, the general character of the country remains the same throughout.
As in Canada, so also in the United States, the Cordilleras are most conveniently divided into natural regions determined by physical features. The Columbia plateau, built up of lava outpourings, receives but a small rainfall, and a large part is semi-desert covered with sage bush. The soil, however, is fertile, and when water can be obtained large crops are produced. The Rocky Mountain region presents a much less desert-like appearance. The topo graphy is more varied, the rainfall greater, and the vegetation richer. The hill-tops are bare, but the lower slopes are well forested and the parks grass-covered. The Great Basin differs in physical structure and climate from surrounding areas. The region is largely semi-desert, but in places there are facilities for irrigation. and the soil is fertile. The Colorado Plateau is in the desert part of the United States. Physical configuration, soil, and climate all make the region one in which very little economic activity is possible. The Pacific Slope is distinguished from the remainder of the Western Cordillera by its physical configuration, its coastal position, its heavier rainfall, its slight range of temperature, and its richer vegetation. As in some of the previous regions several subdivisions must be recognised.
The division of Mexico into natural regions will be discussed later.