The Prairie plains also extend far to the north of the international boundary, and on their northern border merge with the forest-covered plains in central Manitoba and the northern portion of Saskatchewan, which are drained by northward-flowing rivers. These plains in the far north differ from the Prairie plains in the fact that they are forested and acquire greater diversity from the presence of innumerable lakes, several of which are of large size. For convenience we may designate this vast and but little known northern region as the Subarctic Forest plains. Still farther north, where the forest dies away, lie the Barren Grounds, which merge on their northern border with the frozen morasses or tundra of the arctic coastal plain. To acquire just conceptions of the topographic and other characteristics of the several regions of mild relief which make up the Continental basin is a difficult task, as each one is of great extent and possesses many peculiarities of its own, and besides, in two separate regions, each embracing many hundreds of square miles, movements in the earth's crust have occurred of such a nature as to elevate the rocks and give them the general structure commonly found in mountain ranges. Reference is here made to the Ozark uplift in the southwestern portion of the Prairie plains and the Black Hills of Dakota which rise from the Great plateaus. _The Ozark Uplift._--There is an area embracing about 75,000 square miles in southern Missouri, northern Arkansas, and the eastern border of the Indian Territory, in which the rocks have been upraised above the surrounding Gulf and Prairie plains. The uplift, if we imagine it uneroded, would have the general form of an inverted canoe; that is, it would form an elongated ridge, broad and dome-like in the central portion and dying away on all sides into the great surrounding region of undisturbed and essentially horizontal rocks. The major axis of the uplift, although exhibiting a double curvature, has a general northeast and southwest trend. It is about 500 miles long, and in the widest part is approximately 200 miles broad. What the height of the dome would be had the rocks composing it not yielded to the destructive influences of the air or been removed by streams cannot be readily estimated, since the movements of the earth's crust which upraised it occurred at several widely separated intervals with intervening periods of decay and erosion, and downward movements have also been experienced which submerged the region and permitted the deposit of sheets of sediment over it. If the results of the upbuilding agencies had not in a large measure been counteracted in these several ways, the dome to-day would have a height of several thousand feet. In the present condition the deeply eroded dome presents the net result of elevation over subsidence and erosion. The dome-like form is lost, and in its place is a complex series of ridges and valleys. The higher summits now