The Prairie Plains.—A prairie in the current use of the term is a generally level region, either a plain or a plateau, without forests but clothed with a carpet of luxuriant grasses and flowering annuals. A rolling prairie is an undulating or hilly, grass-covered region. The Great plains
of the west-central portion of the Continental basin meet these requirements, and are typical prairies. On their eastern and northern border the Prairie plains merge with the adjacent forested plains, and on the west from Mexico northward to the subarctic forest pass by still less tangible gradations into the more elevated and drier Great plateaus or high plains, where bunch-grass, with bare intervals between the scattered tufts, takes the place of the continuous sod of the true prairies. The reasons for the change from forest to prairie and beyond to the land of the bunch-grass as one travels from east to west across the interior basin, lie in differences in the humidity of the climate.
The Prairie plains have their beginning at the south in Mexico a short distance from the Rio Grande, and are prolonged northward through central Texas, meeting to the north of Red River the forest-covered Ouachita Hills. But to the west of the Ozark uplift the Prairie plains extend northward in a belt about 100 miles wide which expands in Kansas, northern Missouri, eastern Nebraska, Iowa, Illinois, and western Ohio to fully 800 miles. In this highly fertile region, now the most productive agricultural area of comparable size in North America, if not in the world, one may travel in a straight line for nearly 1,000 miles through a land without high hills but pleasingly diversified by undulations of the generally level surface and by winding stream-formed valleys bordered by swelling bluffs, without losing sight of towns, villages, or comfortable farmhouses. In spring this entire region is bright green with pastures and sprouting grain-fields, and in autumn yellow with the harvest. Miles on miles of rustling corn-fields form the most characteristic feature of the summer landscapes.
The Prairie plains contract to the north of Illinois and Iowa to a width of about 200 miles, being encroached upon by the forests of the Great Lakes region, but are prolonged northward through Minnesota and the Dakotas far into Canada. The length of these natural meadows from south to north is nearly 2,000 miles; their entire area is not far from 500,000 square miles. On the north they merge
with the vast region of similar relief which is darkened by the pines and spruces of the subarctic forest.
The northern portion of the original prairie region has been given a new and in some respects a more pleasing aspect by the sowing of millions of acres with wheat. This is the most favourable large area for wheat culture in North America, and one of the three great wheat-growing regions in the world. The most productive portion of these northern wheat-lands lies in the valley of the Red River of the North, situated in part in Minnesota and the eastern portion of the Dakotas, but including also the plains of Manitoba. Could we view the broad extent of the Prairie plains as do the birds in their southward migrations, we would see them golden with the sheen of ripening wheat at the north, green and russet in the central portion with corn, and white with cotton to the south. Everywhere from south to north and east to west the vast expanse is dotted with the curling wreaths arising from household fires, and at hundreds of localities blotted by the smoke of towns, factories, smelting-works, and coal-mines.
Throughout the entire extent of the Prairie plains the underlying rocks are essentially horizontal, and consist largely of limestone. An ancient sea-bottom has been broadly upraised with but slight disturbances of the strata to a general elevation of about 800 feet in Minnesota and the Dakotas. From this low continental divide the land slopes gently both to the north and south. The local variations of surface are due mainly to the unequal weathering of the rocks and the excavation of stream-formed valleys. To the north of the mouth of the Ohio, however, the prairie, in common with the adjacent regions, was formerly occupied by glacial ice, which on melting left widely spread deposits of clay, stones, gravel, etc., which gave the region a new surface, and in certain instances turned the streams from their former courses. Much of the rolling prairie inherits its billowy surface from the glaciers. In the midst of the young topography of glacial and more recent date there is an area of about 10,000 square miles in southwestern Wisconsin and adjacent
portions of Minnesota and Iowa which is surrounded by the deposits of the ancient ice-sheets (glacial drifts), but not covered by them. This driftless area, as it is termed, has an old topography in striking contrast to the relief of the region about it, in which broad river-valleys bordered by the pinnacled and castellated rocks exposed in the bordering slopes of the adjacent uplands are among the most conspicuous features.
The soil of this driftless region is a ferruginous clay, resulting from the prolonged weathering of the rocks, principally limestone, on which it rests, while the surfaces formerly covered by glacial ice are mantled with soil of a mixed character containing many fragments and large boulders of compact rock. In the prairies to the south of the glacial boundary the soils are mainly of a sedentary origin, and have resulted from the disintegration and decay of the rocks on which they rest, but usually rendered black by the humus resulting from the partial decay of numberless generating grasses and other lowly plants. This black soil is wonderfully productive and furnishes the basis of the greater part of the wealth and industries of the region it covers. The minor exceptions to the general fertility occur where the rocks immediately underlying the surface, as in the zinc and lead region of southwestern Missouri, are highly charged with flint-like material, which remains when the limestone once containing it is dissolved and carried away. The horizontal sheets of rock beneath the broad central portion of the Prairie plains belong to the Carboniferous system and contain highly valuable seams of bituminous coal. The area of these coal-producing lands is estimated at 125,000 square miles. In this same region also there are extensive tracts in which natural gas and petroleum are obtained in remarkable abundance. In southern Wisconsin and the adjacent portions of Illinois valuable deposits of lead occur under conditions similar to those associated with the lead and zinc mines about the northern border of the Ozark uplift.
Owing to the demand for transportation facilities and