PHYSICAL AND CLIMATAL CONDITIONS. 117 



hut tlu!S(; are not unlikely iiMdenudod portions of former 

 beds, lie also suppose.s tliein to have been ])Ushed up 

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

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



Dr. IVU informs me that drift deposits containin<^ shells 

 occur on the north of the Laurentian axis, facing' llud.son's 

 bay, in many localities, and that in t)ne of these they 

 reach to within l'X> miles of lake Superior, and are at an 

 elevation of (52') feet, or very nearly that of the lake 

 itself. 



I have already referred to the ol)servations of ]Jr. (}. M. 

 ])awson with reference to the Missouri coleau, one of the 

 j^reatest ridges of drift in the world. Ifis description of 

 it merits (quotation here, as a remarkable example of an 

 old sea marj^in.* 



" The •.,aeat drift-rid<^e 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 (jf a polar ice-cap, or derived from the elevated 

 Laurentian region to the east and nortli ; but I think, in 

 view of the })hysical features of the country, neither of 

 tiiese theories can l)e sustained. 



"To reach the country in the vicinity of the forty- 

 ninth parallel a northern ice-sheet would have to move 

 up the long slojje from the Arctic ocean and cross the 

 second transverse w^atershed ; then, after descending to the 

 level of the Saskatchewan valley, again to ascend the 



* Quarterly Journal London Oeol. Society, 1875. 



