Plain

PLAIN (Lat. p/anum, level ground), a tract of land which is level or undulating. That por tion of the earth's surface not covered by water may be classified into twogreat divisions, This namely, mountains and plains. is broad classi fication includes under plains all broad tracts whose surfaces are not so elevated as to be in cluded among mountains. The plains may be classified as the narrow tracts of land, with high land or mountains bordering the sides, as valleys; the broad expanse of level or rolling land of an altitude of 1,000 feet or over, as a plateau, and all the broad plain-lands below 1,000 feet are classified as plains. This classi fication is not always followed, as many of the plateaus of the world are called great plains. Another method of classification is by the nature of the formation of the plain. The rivers of the world which enter the ocean de posit each year a large amount of debris brought down from the mountains. The ocean currents and tides distribute this deposit, over the ocean bed and, in some places, a constant process of plain-building is in progress. As the amount of soil accumulates, the plain grows higher until it becomes a part of the continen tal land mass. Such tracts of land are called marine plains. The North Atlantic marine plains formed on both the east and west coasts are now so broad that the coast plain on both sides extends far out, below the surface of the water. The fossils found in the strata indicate the origin of the Atlantic Coastal Plain. Tracts of land that were once the beds of great lakes, but which have dried up, are called lacustrine plains. Lacustrine plains exist around Great Salt Lake in Utah, and in Nevada, the valley of the Red River of the North, the vale of Kashmir in northwestern India, and the great Hungarian Plain. The deposit of silt at the mouths of rivers, and sometimes along the banks make fluviatile plains, or flood-plains. The Mississippi, Po, Ganges, Nile and other large rivers have constructed great fluviatile plains, and the mighty builders still continue their work. Still another origin for plains is erosion, by means of which the mountains are lowered and the broad tract of rolling or hilly land forms. Such formations are called plains of denudation. Where considerable of the former mountain area remains, the lowland formed by erosion or denudation is called a peneplain. In respect of fertility plains show all gradations from wholly barren salt plains, such as the sali DaS of Argentina, in South America, and almost wholly barren deserts, such as are represented chiefly in Africa and Asia, to the highly pro ductive alluvial plains of such great rivers as the Mississippi and the Ganges. Various spe cial kinds of plains in different parts of the world are distinguished by special local names. Among these are the landes, or sandy plains in the southwest of France; the treeless steppes of southern Russia in Europe and Central Asia; the marshy tundras of northern Siberia; the arid karroos of Cape Colony; the savannahs and prairies of North America; the grassy llanos of the Orinoco Valley; the forest plains or selvas of the Amazon basin; and the treeless and partly barren pampas of Argentina. The great desert plain of the world is the Sahara (q.v.) in Africa, extending from the west coast of Africa to the Red Sea, a distance of over 2,500 miles; and over 1,000 miles wide from north to south. This desert plain is made of bare ledges of rock miles in extent, oceans of sand, white in some places on account of the salt. Beyond the Red Sea the desert lands extend, including the Arabian plain, and plains in the interior of Asia, into China almost to the Pacific Ocean. It must not be understood, however, that all deserts are plains; many are highly mountainous. The great plains of the interior of Africa, south of Sahara, are covered with dense vegetation. The interior of Australia, so far as known, consists of extensive low plains upon which the waters of the rivers become stagnant amid gigantic reeds and her baceous brushwood. The long dry seasons to which the country is subject make the plains vast deserts. The falling of the rains, however, speedily converts these dusty wastes into verdant pastures. Central Asia is a region of immense mountain chains supporting table lands of great extent. The northern parts of the same continent and of Europe present in a range of more than 6,000 miles a succession of broad plains, covering the greater part of Siberia, a large part of Russia, Germany and Holland. On this range, from the Pacific to the Atlantic, are no elevations exceeding a few hundred feet. These plains in Siberia and Russia are called steppes, and large portions of them are rich pasture lands, without trees, and much resembling the prairies of the Mississippi Valley. The American continent, north and south, is eminently a land of plains. They form full two-thirds of the whole surface of the country, extending on the Atlantic side from one extremity of the continent to the other, with only occasional interruptions by mountain ranges of little extent. In South America are distinguished three great regions of plains separated from each other by low ranges of mountains, which run from the At lantic Coast toward the Andes. The northern of these regions, having an area of 260,000 square miles, comprises the valley of the Ori noco and its tributaries, and the elevation of this great territory nowhere exceeds 300 feet above the sea-level. So smooth is the surface that over hundreds of square miles the land is almost as unbroken by any unevenness as the water 'itself, and the rivers are so sluggish that their current is diverted in any direction by light winds. This is the region of the llanos (Lat. loca plana). In the dry season the ground is parched and barren, and clouds of fine dust and sand incessantly rising fill the air. The grasses, which in the rainy season suddenly spring up and grow to the height of four feet, are withered and crumble into dust. But as the vegetation appears with the return of the rains, the plains are soon overrun by vast herds of horses and wild cattle, which 'then find a rich pasturage; and from the jungles of the river banks, to which they had retired during the drought, the great serpents and alligators make their appearance and overspread the plains. The only interruptions to the dead level of the surface, beside the depressions of the beds of the rivers and creeks, appear to be occasional banks of limestone or sandstone, called Wows, standing four or five feet above the general surface, flat at the top, and several leagues in length. Slight undulations, called mesas, imperceptible to the eye, are indicated by the water-courses which are turned by them in different directions. The plains of the Ama zon extend up the course of that river and its branches to the Andes, and include, with all the waters they enclose and some ranges of bills, an area of 2,340,000 square miles. About one-third of this territory is covered with dense forests, the principal portions of which hive not been explored. So luxuriant is the vegeta tion and enervating the climate, that to reclaim any considerable extent of these wilds is a task almost beyond the ability of man. From their wooded character the plains here are called selvas; but open tracts like• the llanos are scattered among the forests, and numerous broad rivers occupy large areas and afford the only means of gaining access to the distant interior. The plains of the southern portion of South America, lying beyond lat. S., are termed pampas, from an Indian word signify ing a flat. They resemble the steppes of Russia, being open grass-covered tracts of vast extent, interspersed with barren areas composed of rocks and sand. Their total extent from north

to south is about 1,800 miles, and from east to west from 300 to 900 miles. On the north they reach the region of tropical productions, and at the extreme south their surface is in many places concealed beneath the never-melting ice and snow of those frozen latitudes. Across their range from the coast to the Andes three belts are recognized in their northern division, distinguished from each other by their peculiar productions. The first is strongly marked by its singular growth of tall thistles succeeded by clover. The former come forth with wonderful rapidity in the early summer, shooting up to the height of 10 or 11 feet, and bearing a profusion of rich blossoms. So close are the stems, that even if unarmed with their prickles they would still present an impenetrable barrier, As the summer passes away this vegetation dies down, and luxuriant crops of clover spring up, and in vite the return of the countless herds of cattle which were expelled by the thistles. To the west of this is a belt of plains covered with long grass, which from season to season undergoes little change except as the green of summer changes to the brown hue of winter, and this gives place to the verdure of the succeeding spring. Beyond this is a region of more ele vated plains lying along the range of the Andes, and covered with low trees and shrubs, all ever greens. The plains of North America, while no less extensive than those of the southern part of the continent, are distinguished from them by greater diversities of level, which, together with the climate, render the country better adapted to the necessities of man. Excepting the parts cov ered by the Rocky and Allegheny Mountains and their spurs, all the rest are plains uninterrupted by mountain elevations. Near the mountains the surface is hilly and more or less broken, but re ceding from the Alleghenies westward it grad ually assumes the distinctive character of plains, which are developed upon a grand scale in the boundless prairies of the northwest, and in the barren territories commonly known by the name of plains which stretch away from the prairie region in the States of Arkansas, Missouri and Kansas to the foot of the Rocky Mountains. Throughout these immense territories the differ ences of level are sufficient to produce a steady flow in the mighty rivers, not so rapid as to ob struct their navigation, but sufficient to insure salubrity to the country by a healthy drainage; and thus is secured a system of easy intercom munication between all sections of the country, unsurpassed in importance by any similar system in the world. In the first volume of the geolog ical report of Iowa Prof. James Hall has pre sented a full account of the northwestern prairies. The region they occupy is the western part of Ohio, nearly the whole of the States of Indiana, Illinois and Iowa, the southern part of Michigan, the northern part of Missouri and portions of Kansas and Nebraska, in which, near the meridians of 97° and 100° W., they gradually pass into the arid and desert plains. Throughout this territory a great sameness ex-, ists in the varieties of the topography, the vegetable productions, the soil, and geological features. The surface is drained by streams which commence in almost imperceptible de pressions of the high prairies, and flow in beds and valleys of gradually increasing depth be tween vertical walls of limestone or sandstone, through the horizontal strata of which the current has in past times made its channel. What are called bottom lands lie between the rocky bluffs and the stream, and upon the Mississippi and the Missouri, these attain in places a width of six to eight miles; they are, however, often wanting entirely, the bluffs on each side coming close to the river banks. On the upper Mississippi the bottom lands are in gen eral well wooded, but along the State of Mis souri they spread out into open prairies. These low or wet prairies are distinguished from the high or rolling prairies, which form the gen eral upper level of the country upon the sum mit of the bluffs. The elevation of these above the rivers is very variable. Near Prairie du Chien in Wisconsin, it is about 400 feet above the Mississippi, and the bluffs themselves pre sent a vertical face of about 300 feet. At Cairo in Illinois, the upper surface is from 100 to 250 feet above the river, or 400 to 550 feet above the sea-level. In the central portion of the State, near the Illinois Central Railroad, the average elevation is from 650 to 750 feet above the sea, and near the northern border of the State this increases to 800 or 900 feet, and some of the highest swells of the prairie are 1,000 feet high. In southern Wisconsin the more elevated portions of the prairie are about 1,100 feet above tide water. In Iowa the plateau du coteau des prairies of Nicollet, dividing the waters of the Mississippi from those of the Missouri, is from 1,400 to 1,500 feet above the sea. On the head waters of the Illinois and Wabash, and south and west of Lake Michigan, the prairies are very • level and smooth, and are termed flat. Elsewhere the surface is undulating and broken by the depressions of the streams, and they are known as rolling prairies. The de pressions where there are no streams are often 50 feet below the mean level, and in the bottom the soil is wet and marshy and forms ((swales* or which render the roads almost im passable. In these places the grass grows very rank and tall, but upon the upper and drier surface the natural growth is finer and the sod dense and closely interwoven. A great variety of flowering plants are interspersed among the grasses, and during the summer the whole surface of the prairies is gaily decked with bright colors. The characteristic herbs, as described by Professor Gray in a paper on the *Flora of the Northern States,* published in the Journal of Science) (2), xxiii, p. 397 (1857), would seem to be composite,. especially helianthoid composite, of many species. Trees are in scattered groups, or along the larger streams, or occasionally on low rocky ridges. West of the Mississippi they become less fre quent, and near long. 98° W. they disappear altogether. The soil of the prairies is remark able for its finely comminuted condition. It is generally free from stones, though in some lo calities boulders or fragments of rock are found upon the surface and scattered through it. In the swales and in some of the bottom lands the rich black vegetable mold is very deep, but on the upper prairies its depth is usually from one to two feet. The subsoil is almost invariably an argillaceous loam, more or less mixed in its lower portions with sand and occasional pebbles. The total thickness of clay, sand and loam amounts in some places near the larger rivers to 200 feet, but the rock is often found in other places very near the surface. Water is generally found in the sandy stratum 15 to 30 feet below the surface. Throughout the prairie region the underlying rocks are soft sedimentary strata, especially shales and impure limestones. Most of these on exposure disintegrate readily and crumble to soil, and the whole soil of the prairies appears to have been produced from such materials not removed far from their first beds. To the finely comminuted condition of these materials Professor Hall ascribes the less character of the prairies. Where such soils are found in portions of the western part of North America, covering tracts of limited even enclosed in thickly wooded districts, they are commonly without trees; and as is the case with the vast treeless plains of the Mississippi Valley, no ancient trunks buried in the soil indi cate that the localities were ever covered with trees.