180 THE CANADIAN NATURALIST. [Vol. X. 



a theory, wliich they do not. May not this, I would respectfully 

 ask, be nn instance of the danger of yieldini^ undue prominence 

 to lithological characteristics in determining the comparative 

 age of rocks, in the absence of stratigraphical or palaeontological 

 evidence ? 



Some of the high lands in the interior of the location are 

 composed of a different and probably much more recent descrip- 

 tion of eruptive or volcanic rocks than any of those described. 

 Thus at a point about two miles from the southern and one mile 

 from the eastern boundary (or lake shore), a mountain of tra- 

 chyte or phonolite rises to an altitude oP from 800 to 1000 feet, 

 in which tlure occurs a remarkable rift or cavity, evidently con- 

 nected with the dykes or veins which traverse the subjacent 

 rocks, thus proving that the origin of these latter is of a more 

 recent date than that of all the rocks through which they have 

 penetrated. I should add here, en parentlihe, that besides the 

 great dyke and associated mineral veins which I have noticed as 

 occurrinir here, there are distinct traces of the former existence 

 of a great parallel vein, or set of veins immediately to the south, 

 which, by breaking up the continuity of the rocks and thereby 

 weakening them, have given rise to the remarkable deep bay 

 lying immediately to tlie south. 



I have referred to a line of weakness and probable rupturing 

 of the rocks eastwards from the areat rift, fissure or crater in 

 the trachyte mountain, giving origin to the deep peculiar shaped 

 bay, which I have called Mines Bay. If we trace the same line 

 still further eastwards to the other side of the bay, we find a 

 deep narrow channel between the south end of Harrison's Loca- 

 tion and Bead's Island to the Chenal Ecart^, running up from 

 Lake Superior to Nipigon Bay. This narrow channel probably 

 owes its origin to the same cause, namely, the weakness of the 

 rocks forming its bed ; and we may also observe that tlie same 

 metalliferous veins which have been discovered and partially 

 explored on Harrison's Jjocation, correspond in position and 

 direction with those which I have recently discovered, without 

 beinir aware of this relation, on the main land of St. I<i:;nace. 



The intervening great bay has evidently been scooped out by a 

 glacier, as the glacial striae are exceedingly well marked and 

 conspicuous, running exactly parallel with the direction of the 

 axis of the bay ; and they are more strikingly displayed on the 

 hard porphyry rocks than on the softer amygdaloids ; this being, 

 DO doubt, due to the more resisting character or the former. 



