MOUNTAINS, LAKES, AND KIVERS. 



235 



south-eastern flanks they show an abrupt and broken 

 escarpment, and within the space of five miles the country 

 sinks from sixteen hundred to six hundred and eighty feet 

 above the sea, or within eighty feet of the level of Lake 

 Winnipeg. 



At the foot of these hill-ranges, and east of them, lie 

 the great Lakes Winnipego-sis and Manitobah, which are 

 separated from Lake Winnipeg by a low, marshy, and 

 nearly level tract, having an elevation rarely exceeding 

 eighty feet above it. 



The uniformity which obtains in the geographical dis- 

 tribution of the great lakes of the Winnipeg Basin is a 

 beautiful illustration of the dependance of geographical 

 features upon geological structure. It is equalled only by 

 the relations of the great Canadian lakes, whose form and 

 general features have been shown to be determined by 

 the formations in which they are excavated.* 



The outcrop of the different formations in the valley of 

 Lake Winnipeg, as far as they are known, follows the 

 general direction of the rim of the basin in which they are 

 deposited with remarkable uniformity. Conforming to 

 the direction of the Laurentian system exposed on the 

 east side of Lake Winnipeg, aiid constituting the Lauren- 

 tide Mountains, the Silurian series stretches from Pembina 

 on the 49th parallel, to the Saskatchewan on the 54th, 

 and thence towards the Arctic Sea. Following its out- 

 crop, the Devonian series is symmetrically developed 

 between the same distant boundaries ; but the most 

 singular feature of this region is, that the soft Cretaceous 

 shales should also conform, with tolerable exactness, to 

 the exposed edges of the unfossiliferous rim of the great 



* On the Physical Structure of the Western District of Upper Canada, 

 by Sir W, E. Logan, F.R.S. 



