620 G. M. DAWSON ON THE SUPERFICIAL GEOLOGY OF 



bles a gigantic glacier-moraine ; and, marking its course in the map, 

 it might be argued that the nearly parallel line of elevations, of 

 which Turtle Mountain forms one, are remnants of a second line of 

 moraine produced as a feebler eifort by the retiring ice-sheet. 



Such a glacier must either have been the southern extension of a 

 polar ice-cap, or derived from the elevated Laurentian region to the 

 east and north : but I think, in view of the physical features of the 

 country, neither of these theories can be sustained. 



To reach the country in the vicinity of the forty-ninth parallel a 

 northern ice-sheet would have to move up the long slope from the 

 Arctic Ocean and cross the second transverse watershed, then, after 

 descending to the level of the Saskatchewan valley, again to ascend 

 the slope (amounting, as has been shown, to over 4 feet per mile) to 

 the first transverse watershed and plateau of the Lignite Tertiary. 

 Such an ice-sheet, moving throughout on broad plains of soft, uncon- 

 solidated Cretaceous and Tertiary rocks, would be expected to mark 

 the surface with broad flu tings parallel to its direction, and to oblite- 

 rate the transverse watersheds and valleys. 



If it be supposed that a huge glacier resting on the Laurentian 

 axis spread westward across the plains, the physical difficulties are 

 even more serious. The ice moving southward, after having de- 

 scended into the Red-Kiver trough, would have had to ascend the 

 eastern escarpment of soft Cretaceous rocks forming its western side, 

 which in one place rises over 900 feet above it. Having gained the 

 second prairie- steppe, it would have had to pass westward up its 

 sloping surface, surmount the soft edge of the third steppe without 

 much altering its form, and finally terminate over 700 miles from its 

 source, and at a height exceeding the present elevation of the Lauren- 

 tian axis by over 2000 feet. The distribution of the drift equally 

 negatives either of these theories, which would suppose the passage 

 of an immense glacier across the plains. 



In attributing the glacial phenomena of the great plain to the 

 action of floating ice, I find myself in accord with Dr. Hector, who 

 has studied a great part of the basin of the Saskatchewan — and also, 

 so far as I can judge from his reports, with Dr. Hayden, who, more 

 than any other geologist, has had the opportunity of becoming- 

 familiar with all parts of the Western States. 



The glaciating agent of the Laurentian plateau in the Lake-of- 

 the- Woods region, however, cannot have been other than glacier-ice. 

 The rounding, striatum, and polishing of the rocks there, are glacier- 

 work ; and icebergs floating, with however steady a current, cannot 

 be supposed to have passed over the higher region of the watershed 

 to the north, and then, following the direction of the striae and 

 gaining ever deeper water, to have borne down on the subjacent 

 rocks. The slope of the axis, however, is too small to account for 

 the spontaneous descent of ordinary glaciers. In a distance of about 

 30 miles, in the vicinity of the Lake of the Woods, the fall of the 

 general surface of the country is only about 3| feet to the mile. 

 The height of the watershed-region north-east of the lake has not 

 been actually measured: but near Lac Seul, which closely corresponds 



