194 PHYSICAL GEOGRAPHY. 



been already mentioned, on the same level and In the 

 close neighbourhood of the sources of the Mississippi and 

 St. Lawrence. The waters of the lake wash, on the east 

 side of the basin, the " intermediate primitive rocks," and 

 find their way through them by anastomosing channels 

 named Sea River, Katchewan, and in its lower part Nel- 

 son River. After it has passed through the intermediate 

 belt, it takes its way over silurian limestones, and finally 

 enters Hudson's Bay through alluvial deposits of some 

 extent. 



The surface of the lake has been calculated to be 853 

 feet * above the sea, and its basin is excavated in the 

 silurian beds. Along the whole eastern shore the granite, 

 gneiss, and trap rocks are every where exposed, the first 

 named rock being the most extensive ; and nowhere do 

 these masses rise to the altitude of hills. On the north 

 and west the birds' eye limestone is the prevailing rock, 

 and forms low cliffs, in a country otherwise every where 

 flat; and towards the south end of the lake, and in the 

 narrows, arenaceous deposits appear in the immediate 

 vicinity of granite, trap-rocks, and chlorite slates, having 

 a close resemblance to those of Pigeon Bay of Lake Su- 

 perior, where argentiferous veins occur. It is, therefore, 

 an interesting quarter for exploration by the practical 

 miner. 



In ascending from Lake Superior by the Kamenis- 

 tikwoya, and its upper branch named the Dog River, 



* Captain Lefroy's observations: — "In the Geological Appendix 

 to Sir John Franklin's Second Journey, I estimated the height of 

 Lake Winipeg above Hudson's Bay at 800 feet, which I considered 

 to be a rough approximation. Major Long places it at the same level 

 with Lake Superior, and the dividing ridge between the two basins 

 at 600 feet higher ; but, by the best estimates I have been able to 

 orm, he makes the summit of the ridge 230 feet too low." 



