Page:The New International Encyclopædia 1st ed. v. 19.djvu/743

UNITED STATES. We give this name to the lower lands of the Mississippi basin, although it is but a vague designation. These plains pass gradually up into the plateau on the east. To the north they merge with the smooth lowlands about the Great Lakes, to the south they are continuous with the Gulf lands, and to the west they pass gradually into the high plains west and south of the Missouri River. The region is often called, in the same rough way, the Prairies. See.

The lands about the Great Lakes have considerable variety. During the recession of the continental glacier the lakes had higher water levels and often much greater extent than now. During this flooded condition what are now the bordering lands received a cover of such fine muds as are spread upon the bottom of all great bodies of water. To some extent previous inequalities are masked, and the resulting surface is often very smooth and almost level. This is especially true of lakes Ontario, Erie, Huron and Michigan. Some of these lands were treeless and hence were property called prairies, although modern physiography prefers to designate them as lake plains. Lake Superior is surrounded by older rocks, which have been greatly disturbed and metamorphosed, and the remnants of these ancient mountains form a higher and rougher land than about the lower lakes. This is true of the northern peninsula of Michigan, of Wisconsin, and of northeastern Minnesota. Naturally, therefore, these rocks hold vast stores of iron and copper, while the strata of the prairies offer little in the way of mineral resources except coal. See.

These are most simply defined as a continuation of the Atlantic Coastal Plain, or another part of the younger fringe of the continent. In central Georgia and Alabama the younger formations abut on the older rocks of the southern Appalachians and mark approximately the encroachment of the later seas. By gentle uplift the marginal sea bottoms of the Gulf were laid bare, and form the flat lowlands of this semi-tropical region. This explains in brief the origin of the peninsula of Florida, most of whose surface has now an altitude of less than 100 feet. A gentle uplift of the sea bottom brought this land into existence. Cavernous openings in the rocks, underground streams, and springs of great volume result from the presence of extensive limestone formations as part of the bed rock of the region. The seaward edge of this land abounds in sand bars, coral reefs, and mangrove swamps, and this single State, counting its main shores, its bays and numberless islands, has more than 4000 miles of shore line. It is proposed to open a way for quiet water navigation down the entire east coast of Florida.

Westward from Alabama, the (q.v.) becomes the controlling feature in the topography of the Gulf region. The broad Gulf plain occupies a large part of southern and eastern Texas. As in the region to the eastward, the younger rocks have been made into land by uplift and retreat of the sea. As a rule the surface slopes gently toward the Gulf, but with escarpments and great local variations of topography. Some areas are prairie, while others are heavily forested, and the rise to the northwest leads first

to the great plateau, or Llano Estacado, and then to the mountains of the Rocky Mountain Range. The shore line is a long crescent, bordered by extensive sand bars, which inclose stretches of quiet water. Galveston is on one of these bars, and it is thus exposed to the Gulf hurricanes.

This is the name usually given to the lands which rise gradually from the prairies to the eastern base of the Rocky Mountains. But the altitude of these lands is such that they might be called with propriety a plateau. From altitudes of about 1000 feet along the Missouri River in Kansas and Nebraska, they rise to heights of 5000 to 6000 feet at the foot of the western mountains. In general this rise is imperceptibly gradual, but its continuity is sometimes interrupted by escarpments, and the easterly flowing rivers have incised shallow valleys upon the region. The strata are little disturbed and thus the country resembles the prairie region, but the underlying beds are geologically younger and are overlain in many areas by large bodies of waste, which in part may have been deposited in lakes and in parts was no doubt distributed by torrents from the mountains. Climatic causes have also made the region different in aspect from the prairies. The plains are semi-arid in the east and truly arid in the west, and are therefore but sparsely clad with vegetation. Forests are thus infrequent, the herbaceous vegetation is sparse and has the character of the desert, and agriculture as one goes west is dependent on irrigation. Over large areas the water supply for this purpose is deficient, and grazing is the only remaining resource. This region is a vast one, having the east and west limits already given, and reaching from central Texas to the northern border of the country, where it merges into the great Western plains of Canada. In the north the most prominent break in the plains is the Black Hills mountain area. Here an elevated mass of ancient rocks protrudes through the younger strata, giving a region of rugged relief, hard rocks, mines, and forests. In the Black Hills region, in much of the western Dakotas, and in Montana and western Nebraska, are the (q.v.).

There is yet to be noticed the most extensive body of elevated land between the Appalachians and the higher levels of the great plains. This lies in southern Missouri and in northern and central Arkansas and westward. In Missouri these uplands are of moderate height, dissected by the rivers, covered with forests, and known as the Ozark Plateau. Still better known, owing to their metallic deposits, are some low mountains of very ancient rocks familiar as Iron Mountain and Pilot Knob. Running through central Arkansas are the Ouachita Mountains. These rise from below the young sediments of the Mississippi Valley, and trend westward, passing through Indian Territory and Oklahoma into northern Texas. This upland region south of the Missouri River, therefore, is associated on various sides with the prairies, the alluvial plains of the Mississippi, the Gulf plains of the South, and the great plains of the West.

The name is properly applied only to an eastern range of the Cordilleran or Western Uplands. The range, with numerous peaks rising above 14,000 feet,