216 PROCKEDINGS OF THE GEOLOGICAL SOCIETY. [Jail. 4, 



The map (hitherto unpubUshed) which accompanies this paper is 

 taken from the archives of" the Canadian Boundary Commission, 

 whose surveyors I accompanied in their circumnavigation of this 

 lake. While they were employed on its topography, I attended to 

 its geology. 



Geological conditions. — The geology of Rainy Lake is well 

 worth a short but careful notice, because it continues north-easterly, 

 into a country rarely visited, the investigations of Dr. Norwood, of 

 l)r. Dale Owen's party of geological surveyors, who worked to the 

 north-east from the head-waters of the Mississippi. Professor Keat- 

 ing (Long's Expedition) and Dr. Norwood passed along the south 

 shore only of this lake, and their observations are contained in a few 

 lines*. 



The geology cf this body of water may be summed up in the 

 following words. Chloritic and greenstone slates, gneiss and mica- 

 slate, in proportional quantities in the order here set down, seem 

 once to have occupied the lake-basin, with an E.N.E. strike, and a 

 N.N.W. dip, at a high angle usually. But subsequently a very 

 extensive outburst of granite, with some syenite, has taken place, to the 

 great disturbance of the stratified rocks, and penetrating them both in 

 intercalations and crosswise. These intrusive rocks occupy a very 

 large portion of the lake ; most of the western shore, nearly all the 

 eastern trough or arm, and much of the east end of the lake about 

 Stokes and Hale Bays ; as will be best seen by referring to the Map. 



Near the head of Rainy River, there are vestiges of an Upper 

 Silurian limestone, which will be mentioned in the sequel. 



The whole of Rainy Lake may (solely for the convenience of 

 description and reference) be distributed into six parts, in the order 

 of our voyage round it; each having its own geological characteristic. 



The first includes the whole west side of the lake from Rainy 

 River to Manitou River, and round to Cape Chamberlin. The 

 second takes in the interval of thirty-six miles between Cape Cham- 

 berlin and Cape Bayfield. 



The third embraces the whole eastern arm, — the eight miles south 

 of Point Lyon excepted. 



The fourth occupies fifty-two miles of coast by Barclay and Seine 

 Bays, easterly to near Point Franklin. 



The fifth includes the whole south-eastern end of the lake, a coast- 

 line sixty miles long, and having Point Franklin and Maypole Island 

 as its western limits. 



The sixth portion takes in the south shore from Maypole Island 

 to Rainy River. 



First Division of the Lake Shore. — The first of these portions 

 or divisions (west shore), with the exception of a small district 

 of greenstone slate at the south angle of Peche Bay, running ob- 

 scurely E.N.E., is mainly occupied by granite ; this is coarse in grain 

 and grey about Peche Bay, but north of Otter Point the prevaiUng 

 colour, especially in Manitou Sound, is white, from that of its three 



* See Dr. D. Owen's Report of a Geological Survey of NViscoiisin, losva, and 

 Minnesota, &c. 4to. Philadelphia, 1832. 



