284 ASSINKIBOINE AND SASKATCHEWAN EXPEDITION. 



very elongated bay.* Sweeping round the south and 

 part of the west coast of the Lake of the Woods, it leaves 

 that body of water and comes on the Winnipeg, above 

 Fort Alexander. The south and west coasts of Lake Win- 

 nipeg, and as far as its north-east corner mark the easterly 

 boundary of this basin ; it then passes north of Moose Lake, 

 to Beaver Lake, and thence in a north-westerly direc- 

 tion towards and beyond Methy Portage. The Silurian 

 rocks of Great Slave Lake and Eiver present forms chiefly 

 belonging to the upper division of the series. The occur- 

 rence of brine springs in that region points also to the 

 proximity of Devonian rocks, which are particularly cha- 

 racterized by brine springs in the basin of Lake Winnipeg. 

 The upper Silurian rocks of the Arctic Archipelago rest 

 everywhere on granitoid rocks with a remarkable red 

 sandstone passing into' coarse grit for their base.f 



Limestones, sandstones, and shales of Silurian age are 

 exposed from the Grand Eapid of the Saskatchewan to 

 Big Black Island, near the south extremity of Lake Win- 

 nipeg. From Big Black Island to the rapids on Eed 

 Eiver the formations are concealed by quaternary de- 

 posits. On the south-east coast limestone is occasionally 

 seen in position, but its junction with the Lauren tian series 

 near the mouth of the Winnipeg is concealed by drift. 



The formations which have been recognized on Lake 

 Winnipeg, and in the valley of Eed Eiver, are 



1. The Chazy Formation. 



2. The Bird's-eye „ 



3. The Trenton 



4. The Hudson Eiver Group. 



* See 11 Geology of the Lake of the Woods." — Dr. Bigsby, Quart. Journ. 

 Geo. Soc. vol. viii. p. 406. 



t Rev. Samuel Haughton, F.R.S., Appendix to Capt. M'Clintock's Nar- 

 rative. 



