From Atlantic to Pacific, the breadth of the United States is not less than twenty-five hundred miles; and from north to south the country extends nearly seventeen hundred miles.
Surface.—The surface of the United States from east to west may be divided as follows: (1) The Atlantic Plain, which extends from the coast to the Allegheny Mountains. (2) [580] The Mississippi Valley and Great Central Plain, which extends from the Allegheny Mountains west to the Rocky Mountains. (3) The Western Highlands. (4) The Pacific slope, which extends from the Rocky Mountains to the Pacific Ocean.
Mountains and Plains.—The chief mountain systems are the Appalachian region in the east and the Rocky Mountains in the west.
The Appalachian System begins in the northern part of New England (in Maine without the appearance of regular ranges) and New York, and extends southwestward to Alabama and Georgia, being divided by the Hudson River valley and Lake Champlain, and that of the Mohawk River into three distinct sections.
A coast-plain extends from its eastern base to the Atlantic. It is narrow in Maine, where it terminates in a bold rocky coast indented by bays, and broken into projecting promontories and islands. South of Massachusetts the coast becomes lower and more sandy, and the plain grows gradually wider, with the exception of a narrow belt at New York, until in North Carolina it attains a width of two hundred miles.
In the southern part of New England it is characterized by hills, and below New York by a distinct coast region and a more elevated slope. This higher region, which is in Virginia and thence southward, is marked by a somewhat abrupt terrace, varies in altitude from a few hundred to more than a thousand feet, and is known as the Piedmont plateau. The lower coast region is seldom more than one hundred feet above the sea. It has a sandy soil, and in many places there are large swamps near the coast. Much of this swampy country is uninhabitable, but when reclaimed, as it has been in many parts of North and South Carolina, it makes valuable rice-land. Many acres of fertile agricultural land have also been secured in Florida by draining its swamps. The middle elevated region is diversified by hills and valleys, and has a productive soil. The dividing line between it and the low coast-plain marks the head of navigation of most of the streams, and also determines the sites of many important towns.
The surface of this region today is a series of parallel ranges divided by fertile valleys. The various ridges are named as follows: The Blue Ridge, which lies nearest the Atlantic; the Kittatinny Chain; the Allegheny Mountains, which lie in the western part of Virginia and the central part of Pennsylvania; the Cumberland Mountains, on the eastern boundary of Tennessee and Kentucky; the Catskill Mountains, in the State of New York, which are continued in the Sacondago Chain; the Green Mountains, in the State of Vermont; the Hudson River Highlands, and the hills of New Hampshire. There is no peak of marked elevation in the Appalachian region, the highest point being Mt. Washington, in New Hampshire, which reaches a height of nearly seven thousand feet.
Great Central Plain.—West of the Appalachian system and lying between it and the western highland is a great central valley, forming part of the continental depression which extends from the Arctic Ocean to the Gulf of Mexico. It is almost an absolute plain, rising gradually from the Gulf toward the chain of Great Lakes in the north, and toward the mountains on the east and west. The only important departure from its uniform level character is an elevation of from five hundred to two thousand feet, running from southern Missouri through northwestern Arkansas into eastern Oklahoma, and known as the Ozark Mountains.
This great valley occupies about one-half the entire area of the United States, and the fertile prairies and bottom-lands of the eastern and central portions make it the most important agricultural basin of the globe. From an irregular line west of the Mississippi River the land rises in an almost imperceptible slope till it reaches the base of the western plateau.
The Rocky Mountain System extends a distance of about two thousand miles. The system is continued in Canada. The Rocky Mountains are not a single range, but are double and sometimes threefold. These ranges are the edge of a region of plateaus and hills which extends to the coastal mountains. The chief mountain ranges belonging to the United States Rockies are the Bitter Root Mountains, the Blue Mountains, and the Big Horn Mountains in the north; the Wahsatch Mountains, the Wind River Mountains, and the White Mountains in the center; and the Sierra Madre and the Sangra de Cristo Range in the south. In the western part of the southern Rockies lies the Great Basin of Colorado, with the Wahsatch Mountains on the east and the Sierra Nevada on the west. This basin is extremely arid, has suffered much volcanic action.