It is a kind of world apart, says an American writer; a large valley which seems to have been excavated, in the first place, by an immense vertical out-throw, and then modelled by the prolonged and incessant action of denudating agents. With a mean breadth of 28, and a total length of 90 miles, it develops itself in a westerly direction, at the foot of the sombre mountain-chain known as the _Black Hills_. On issuing from the immense, uniform, and monotonous prairie, the traveller finds himself suddenly transported, after a descent of 100 to 200 feet, into a depression of the soil where rise a myriad of abrupt rocks, irregular or prismatic, or like columns dressed with enormous pyramids, and from 110 to 220 feet in height. [Illustration: VIEW OF THE "MAUVAISES-TERRES," NEBRASKA, U.S.] These natural towers are so multiplied over the surface of this extraordinary region, that the roads wind through them in narrow passages, and the labyrinth may be likened to the irregular streets and narrow alleys of some mediæval European city. Seen from afar, the interminable succession of rocks resembles the massive monuments of antiquity; nor are turrets wanting, nor flying buttresses, nor graceful arches, nor vaulted portals, groups of columns, façades, and taper spires. If at one place the eye lights upon the ruins of a feudal fortress, at another it surveys the graceful ensemble of a Saracenic mosque. Or you might almost say, in the distance, that it is a fantastic "city of the dead" which looms before you; or the gigantic palace of a race of unseen beings, fashioned by the power of spell and enchantment. And if the illusion vanishes when, descending from the heights, you penetrate into the mazes of this Dædalian marvel, the reality is not less calculated to inspire you with astonishment, and the imagination remains confused before this wild, this grand, yet ominous freak of Nature--ominous, for the place seems like a colossal Golgotha, and the rocks may be the monuments consecrated by invisible hands to the things and creatures, the life and majesty, of a forgotten Past! A spectacle unexpected by the European traveller comes at intervals to heighten and confirm the illusion. Here and there are reared constructions of manifest human work, but of a truly primitive character. They consist of four poles, supporting a rude platform of wicker. Mount any adjacent hillock, and you will see corpses and human skeletons outstretched upon the platform. These constructions are, in truth, the burial-places of the Sioux Indians, who wander still in the neighbouring districts.