shadows of evening fill the gorges and ravines, the most unimaginative traveller sees in the silence about him the ruins of a vast city, with cathedrals, temples, and palaces of varied colours and weird designs such as no mortal hand ever fashioned. It is at such times that the picturesque and gorgeous, although desolate, landscape kindles the fancy and suggests day dreams which distract one's attention from the more prosaic study of these earth ruins.
The best developed portions of the strange region here referred to occur on the borders of the uplands overlooking the larger valleys, excavated by the rivers flowing eastward from the mountains, and are simply larger examples of erosion, such as may be seen in many bluffs and valley-sides in nearly every country, but rendered conspicuous by their size, extent, endless variety, and unusual colours.
Sand-Hills.—The sands winnowed by the winds from the bare plains and steep bluffs are in certain places on the Great plateaus gathered into dunes which cover great areas with a succession of low dome-shaped hills. On the borders of the Niobrara River there is a detached area of about 20,000 square miles, which has been covered in this manner with loose sands. This region, as described by F. V. Hayden, presents a succession of round-topped hills, some of them scooped out by the swirling winds so as to resemble volcanic craters. These sand-hills were formerly a favourite resort of the bison, which fed upon the scanty but very nutritious grasses in the little valleys and intervals among the mounds and ridges. There is, for the most part, an abundant supply of water in the lakelets scattered through the region, and fed by the seepage from the porous sands, which drink in all the water that falls upon them and allow it to percolate slowly into the adjacent depressions. Some of the lakelets and ponds are highly alkaline, while others are fresh; the former can be easily distinguished from the latter by the absence of vegetation about their borders. The hills, although seemingly utterly desolate, on a nearer view sometimes reveal considerable vegetation, including yuccas or "Spanish needles," which shelter the sands from the winds.
Many other regions on the western border of the Great plateaus, in the valleys of the Rocky Mountains and on the desert plains of Utah, Nevada, and California, are buried beneath drifting sands, which have the characteristic features of a dune-covered seacoast. The sources of the sands in these interior plains are usually to be found in the disintegration of the rocks under the action of the dry air with its many and sudden changes of temperature, but occasionally they come from desiccated lake beds not yet clothed with vegetation.
Central Portion of the Great Plateaus.—The State of Nebraska, about 400 miles in length from east to west, and extending across the Great plateaus to within some 60 miles of the mountains bordering them on the west, furnishes a typical example of the west-central portion of the interior Continental basin. As described by Hayden, this State may be divided into two portions, one agricultural and the other pastoral. The eastern part, included in the Prairie plains, contains some of the most beautiful, gently rolling, and fertile agricultural lands in America. But the western part is a treeless, almost waterless plain; yet thick, low, sweet, nutritious grasses cover the entire surface, and render it well adapted for the raising of large numbers of horses, cattle, and sheep. Over western Nebraska not more than 15 or 20 inches of moisture fall annually; the snows of winter are very light and soon pass away, the winds rapidly gathering them into the valleys and gorges, leaving vast areas entirely bare. The grasses, instead of decaying, as in all temperate countries with a humid climate, slowly wither, retaining all their nutritious qualities, and thus continue until April or May, when the fresh shoots spring up, so that all kinds of stock thrive throughout the winter on the open plains without artificial shelter. In this account, however, the author cited fails to note that the winters are frequently marked by exceedingly severe storms termed blizzards, during which gales blow while the temperature is far below freezing, and that at such times cattle have been known to perish by thousands.
In late summer and autumn the streams in this portion
of the plateau region for the most part become dry, although water may usually be discovered at long intervals in pools in their beds. In ascending the valleys the water appears and disappears as if by magic. Here one finds a swift-running stream several yards broad, and then for a considerable distance nothing is to be seen but a dry and dusty creek bed, resembling a sunken roadway. Even the broad Platte has so far forgotten itself for several seasons as to cease to be a running stream. It is not uncommon for a river originating in the mountains on the west to be considerably larger towards its source than near its mouth. Many of the important streams that flow from the Black Hills towards the Missouri are lost on their way through the plains. The Yellowstone and the Missouri, the two most important rivers crossing the Great plateaus in the northern portion of the United States, retain their existence throughout the year, although becoming greatly shrunken in autumn, and send eastward a never-ceasing tribute to the Mississippi.
Northern Extension of the Great Plateaus.—The Great plateaus cross the United States-Canadian boundary and extend northwestward through the western portion of Assiniboia and Saskatchewan, and embrace nearly the whole of Alberta and western Athabasca. At the international boundary the plateau region is about 470 miles broad, and extends from longitude 103° 30' westward to the foot-hills of the Rocky Mountains, and in this region embraces what is frequently termed the third prairie steppe, known in part as the Missouri Coteau. The east border of this high plateau throughout much of its extent is well marked by an escarpment which descends some 300 or 400 feet to the second prairie steppe, which together with the first or most easterly of the series, embracing the Red River Valley, is usually considered as belonging to the Prairie plains. The third steppe in the series, or the one extending from the Red River to the Rocky Mountains, has an elevation along its eastern border of about 2,000 feet, rises gradually to the westward, and attains a general elevation of over 4,000 feet on its western border. All of the region of the Great
plateaus north of the international boundary, with the exception of about 20,000 square miles tributary to the Missouri, is drained by rivers flowing eastward to Hudson Bay or northward to the Arctic Ocean. It is thus a portion of the northern or arctic slope of the Continental basin. The eastern border of the plateau country trends northwestward, and finally reaches the Rocky Mountains in the vicinity of the head waters of the Mackenzie, but as this region is but imperfectly explored, our knowledge of the boundaries of the natural division of the continent we have been endeavouring to trace there becomes indefinite. The Great plateaus in Canada merge into the Prairie plains bordering them on the east, and in large part the position of the dividing line between the two is arbitrary.