^°189^0."'] PROCEEDINGS OF THE NATIONAL MUSEUM. 459 



nental region is about 800 feet ; the lowest part being that surrounding the Winni- 

 peg group of lakes, which have an elevation of about 700 feet. From this it slopes 

 up southward, and attains its greatest elevation — 960 feet — at its termination far 

 south in Minnesota. The edges of this prairie level are also, notwithstanding its 

 apparent horizontality, considerably more elevated than its central line, whicb is 

 followed by the Red River. Its width on the forty-ninth parallel is only 52 miles; 

 its area, north of that line, may be estimated at 55,600 square miles, of which the 

 great system of lakes in its northern part— including Lakes Winnipeg, Manitoba, 

 Winnipegosis, Cedar, and St. Martin's— occupy 13,900 miles. A great part of this 

 prairie level is wooded more or less densely, and much of the low-lying land near 

 the great lakes appears to be swampy and liable to flood. The southern part, 

 extending from the boundary line nearly to the south end of Lake Winnipeg, includes 

 the prairie of the Red River valley, with an area of about 6,900 square miles; one of 

 the most fertile regions, and, at the same time, the most accessible portion of the 

 Northwest. 



The superficial deposits of this stage are chiefly those of a great lake which occu- 

 pied its area after the glacial submergence. This part of the interior of the conti- 

 nent being the last to emerge from the Arctic waters and having been covered for a 

 long time afterward by a sea of fresh water, held back either by drift deposits or by 

 rocky barriers, which have subsequently been cut through, and which must have 

 united all the lakes now found in the region into one sheet of water, which extended 

 with narrower dimensions about 200 miles south of the boundary line. 



The Red and the Assiniboine Rivers and their tributaries have not yet cut very 

 deeply into its alluvial deposits and its surface is level and little furrowed by denu- 

 dation. 



The second steppe of the plains is bounded to the east, as already indicated, and to 

 the west by the Missouri coteau, or edge of the third prairie level. It has a width 

 at the forty-ninth parallel of, probably, 200 miles, though it can not there be strictly 

 defined. Its total area is about 105,000 square miles, and includes the whole eastern 

 portion of the great plains, properly so called, with an approximate area of 71,300 

 square miles. These occupy its southern and western portions, and are continuous 

 westward with those of the third prairie steppe. To the south, the boundaries of 

 this region appear to become more indefinite, and in the southern part of Dakota, 

 the three primary levels of the country, so well marked north of the line, are proba- 

 bly scarcely separable. The rivers have acted on this region for a much longer time 

 than on the last-mentioned, and are now found flowing with uniform currents in 

 wide ditch-like valleys, excavated in the soft material of the plains, and often 

 depressed from 100 to 300 feet below the general surface. In these the comparatively 

 insignificent streams wander from side to side, in tortuous channels, which they only 

 leave in time of flood. The surface of this prairie steppe is also more diversified than 

 the last, being broken into gentle swells and undulations, partly, no doubt, by the 

 action of denudation, and partly, also, as will appear, from the original unequal depo- 

 sition, by currents and ice, of the drift material which here constitutes the super- 

 ficial formation. The average altitude of this region may be taken at 1,600 feet, 

 and the character of its soil and its adaptability for agriculture difl'er much in its 

 different portions. 



The thii-d or highest prairie steppe may be said to have a general normal altitude 

 of about 3,000 feet, though its eastern edge is sometimes little over 2,000 feet and it 

 attains an elevation of 4,200 feet at the foot of the Rocky Mountains. 



Obviously none of the third steppe would Ml within our limits were 

 it not for a curious exception that is presented by the Turtle Mountain, 

 which, though belonging to the third steppe, stands like an island upon 

 the open sea of the second. Of this Dr. Dawson says : 



Turtle Mountain, an outline of the third prairie steppe, is a broken, hilly, wooded 

 region, with an area of perhaps about 20 miles square (400 square miles), and slopes. 



