PHYSICAL AND CLIMATAL CONDITIONS. 117 



but these are not unlikely undenuded portions of former 

 beds. He also supj^oses them to have been pushed up 

 from the sea by an ice-sheet, which, however, I am sure, 

 if consulted, would refuse to do him any such service. 



Dr. Bell informs me that drift deposits containing shells 

 occur on the north of the Laurentian axis, facing Hudson's 

 bay, in many localities, and that in one of these they 

 reach to within 133 miles of lake Superior, and are at an 

 elevation of 625 feet, or very nearly that of the lake 

 itself. 



I have already referred to the observations of Dr. Gr. M. 

 Dawson with reference to the Missouri coteau, one of the 

 greatest ridges of drift in the world. His description of 

 it merits quotation here, as a remarkable example of an 

 old sea margin.* 



" The great drift-ridge of the Missouri coteau at first 

 sight resembles a gigantic glacier-moraine ; and, marking 

 its course on 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 effort 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 



* Quarterly Journal London Geol. Society, 1875. 



