606 g. M. DAWSON ON THE supekficial geology oe 



found at the foot of the lowest of the great escarpments already 

 mentioned, which in the vicinity of the boundary-line is known 

 as Pembina Mountain (fig. 1), and, though broken through by the 

 Assineboin river, is continued northward in the Biding, Duck, and 

 Porcupine Mountains. 



Rising to the summit of the second prairie-steppe, we find our- 

 selves on the margin of the " Great Plains," properly so called. 

 This plateau has an average elevation of about 1600 feet, and is 

 bounded to the west by the Missouri Coteau and foot of the third 

 prairie-steppe. On the forty-ninth parallel it has a width of 230 

 miles, on the fifty-fourth of about 200 miles, though it cannot there 

 be so strictly denned. 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 probably scarcely distinguishable. The elevated region lying 

 south and west of the Lake of the Woods, and forming in one place 

 the eastern boundary of the lowest prairie, also assumes the form of 

 a plateau ; and though having an elevation of from 1000 to 1600 

 feet only, it corresponds with the height which the second plateau 

 above described might be expected to have, had it continued thus 

 far eastward. It is covered to a great depth with drift materials, 

 and may be called the drift plateau of Northern Minnesota. 



The third or highest prairie-steppe has an altitude of about 2500 

 feet where it is first met with ; its surface, however, is much less 

 uniform and more weathered than that of the lower plains ; and to- 

 ward the base of the mountains it rises on the boundary-line to a 

 height of 4200 feet, and in the latitude of the North Saskatchewan 

 to about 3000 feet. Southward, as is well known, the plains along 

 the base of the mountains continue to increase in elevation, the level 

 of the passes through the range being equally affected. 



The eastern escarpment of this highest steppe (fig. 2) crosses the 

 boundary-line about longitude 103° 30*, and runs thence with a 

 general west-north-west course to the elbow of the South Saskatche- 

 wan in longitude 108°. Here it bends abruptly, and, passing due 

 north, crosses the North Saskatchewan river. 



Disregarding the two escarpments (which in reality account for 

 but a small part of the westward increase of elevation) and drawing 

 a line in the direction of the greatest general slope of the prairie- 

 surface, from the intersection of the eastern base of the Pocky 

 Mountains and the forty -ninth parallel to a point on the first prairie- 

 level near the northern end of Lake Winnipeg, we find that it crosses 

 the escarpments nearly at right angles, and has an average fall of 

 5-38 feet per mile. A second line starting at the same point, and 

 terminating eastward in the lowest part of the Red-River valley, on 

 the forty-nintli parallel, shows an inclination of 4-48 feet. 



In the foregoing brief summary of the physical features of the 

 region, I have been guided not only by the facts obtained by the 

 Boundary- Commission Surveys, but by the observations of previous 

 explorers, among whom Dr. Hector deserves special mention. To 

 this geologist (who accompanied Capt. Palliser's expedition) is due 



