BAD LANDS, a name applied to portions of the arid regions of the west, which present wide areas of hills and ridges of moderate height, bare of sod and intricately broken by numerous and ravines. The principal areas are in the western Dakotas and central Wyoming and smaller -examples of bad-land topography are of frequent occurrence in the and regions in various portions of the world. In the Big Bad Lands of western South Dakota, east of the Black Hills, there is an area of about 2,000 square miles which consists largely of bad lands occupying extensive basins cut in a plateau along the White and Cheyenne rivers. They present wonderfully weird scenery, but are visited by the average sightseer. An extensive area in the valley of the Little Missouri River is crossed by the Northern Pacific Railroad in the vicinity of Medora and many bad-land features are visible near the railroad. Typical bad lands present ridges and mesas from 200 to 400 feet high in greater part, eroded into fantastic shapes and cut by ravines and gullies into an endless variety of rugged buttresses and pinnacles. The mate rials are mainly light-colored,. sandy clays and soft sandstones in nearly horizontal strata and their bare slopes are dazzling in the bright sunlight. Most bad land regions were table lands originally and areas of the old surface remain in level-topped, grass-covered mesas of various sizes, with bad land slopes extending to flat-bottomed valleys of greater or less width. Bad lands exhibit clearly the close re
lations of topographic form to rock texture, the homogeneous clays being carved into regu lar slopes in which sandstone layers give rise to benches or protect columns and pinnacles of clay. Bad lands are developed in soft rocks where a region has been so uplifted that there is rapid erosion, under arid or semi-arid climatic conditions. The occasional rains cut gullies which eventually are deepened into ravines and, as the rocks are soft, the erosion progresses more rapidly than vegetation can establish itself. In regions of abundant rain fall, vegetation is so vigorous that it usually forms a protective mantle on all but the steeper slopes, but in arid lands a thin sod is the principal growth and it is quickly removed by the rapid run-off of the torrential rains. The Big Bad Lands of South Dakota have yielded large numbers of fossil animals of late Eocene age, which have made the region famous as a collecting ground.
N. H. DArroN, United States Geological Survey.