174 THE CANADIAN NATURALIST. [Vol. X. 



the sunken rocks, much caution and vigilance have to be exer- 

 cised in approaching them by bouts. The camping ground 

 whicli was selected by me, towards the south-eastern end of the 

 location, is a good example of one of these harbors, and is ia 

 fact the only safe one on the place. 



The geological structure of this part of the island (and I 

 bwilcve it is nearly the same throughout) is extremely simple, and 

 will be readily understood. A deep bay running north and south, 

 (8t. Ignace Bay) and forming the eastern boundary of the loca- 

 tion, cuts the rocks transversely and affords an excellent natural 

 Fection. The rocks belong to what is designated by Sir William 

 Logan the upper group of the Upper Copper-bearing Rocks of 

 Lake Superior, corresponding to the Keeweenian Formation of 

 Dr. Hunt; and are regarded by Sir William as the equivalents 

 of the metalliferous rocks of the Eastern Townships of Lower 

 Canada, which he has denominated the Quebec Group of the 

 Lower Silurian system. They form part of the same series in 

 which the great native copper mines of the South Shore of the 

 Lake have been opened up; and there seems no reason to doubt 

 that they are of volcanic origin. The rocks of the location under 

 notice are probably at the extreme upper part of the formation. 



The prevailing rock of the country is a granular amygdaloid 

 trap or melaphyre,* consisting of a small-grained mixture of 

 dark brown feldspar, with angular grains of dark-green chloritic 

 mineral, probably delcssite. It varies frequently in its structure, 

 and the upper part, to which this notice refers, contains amyg- 

 dules, or small spherical masses or nndules of calcspar and deles- 

 site. To this it may be added that quartz, chiefly in the form 

 of agate, jaspar and amethyst, is of frequent occurrence in the 

 amygdules, as also epidote, prehnite and laumontite, with vari- 

 ous zeolite minerals. It is to this rock also that the metals would 

 seem chiefly to belong; such as copper and silver, both native 

 and sulphuretted, also magnetic and specular iron ; although 

 workable deposits of these metals are only to be looked for in 

 veins traversing the rocks, or at the planes of junction between 

 them and another description of rock; and it is to be remarked 

 that the vein stones are always composed of the same minerals as 

 are found in the amygdules. 



* According to the description given ])y Mr. Thomas Macfarlane, of 

 corresponding rocks occurring at Mamainse. See this Joornal, Vol. VII 



