NORTH SHORE OF LAKE SUPERIOR. 189 



Michipicoten Bay, at the Otter's Head, and at the bottoms 

 of Nipigon and Thunder Bays, projecting also in various 

 capes between them. From the last named bay it 

 stretches across the northern bend of the Kamenistikwoya 

 River, by which stream the canoe navigation to the interior 

 is carried on. 



Mr. Logan considers the granite, which frequently 

 passes into gneiss, as the base of the series of rocks com- 

 posing this bank of the lake. 2. To this succeeds gneiss, 

 and both are traversed by dykes and veins of granite. 

 3. The next in order are dark green talcose slates, and a 

 pebbly and slaty conglomerate. 4. Besting unconform- 

 ably on these, is a series of bluish shales, interstratified 

 with trap. 5. Lastly, white or spotted sandstones, indu- 

 rated marls, and conglomerates interstratified with trap. 

 Trap dykes in vast numbers traverse all the beds down 

 to the granite. Veins containing copper, lead, zinc, and 

 silver, belonging to two systems, — one coincident with the 

 rock masses, the other parallel to them, — occur in very 

 many places on the north shore. The courses of the 

 veins vary in different bays, and Professor Agassiz has 

 shown that the outline of the lake has a close connection 

 with the directions of the trap dykes, of which he describes 

 six different systems, each of them associated with one of 

 the great curvatures or bays. 



A granite porphyry, which is very durable, forms a 

 considerable portion of the boldest and most barren parts 

 of the north shore of the lake ; the projections of amyg- 

 daloid, being more perishable, assume the most picturesque 

 shapes ; and some of the loftiest headlands are thickly 

 capped with greenstone, basalt, and other trappean rocks. 

 The low, flat, well-wooded islands are mostly sandstone. 

 The general elevation of the northern brim of the Lake 

 Superior basin may be stated at between 800 and 900 



