of Lake Superior. 259 



Mr. Thompson informs me that the rocks of the north main, 

 between the Grand Portage and the River St. Louis are chiefly 

 composed of hornblende. The cliff, sixty miles east of that river is, 

 probably, greenstone trap. He adds, that at fourteen miles and four 

 miles and a half east of the same river, granite makes its appearance. 



I now subjoin a hasty outline of the geology of the south shore of 

 Lake Superior. From Mr. Schoolcraft we learn that the south shore 

 is, on the whole, sandy, from Point Iroquois to the Pictured Rocks ; 

 that, in this interval, the Sand Hills (" Grandes Sables") immedi- 

 ately west of the Grand Morais, (ninety-three miles trom St. 

 Mary's) present to the lake for nine miles a steep acclivity 300 

 feet high, composed of light yellow siliceous sand, deposited in 

 three layers 150, 80, and 70 feet thick respectively, the last-men- 

 tioned being the uppermost, and like the lowest, pure, while the 

 middle bed has many pebbles of granite, limestone, hornblende, 

 and quartz. Three leagues west from this scaur, the Pictured 

 Rocks commence; and continue for twelve miles along shore. 

 They also are 300 feet high, are stratified horizontally, of a gray 

 colour in the fresh fracture, but stained by the weather of various 

 tints. They consist of a calcareous cement enclosing coarse grains 

 of sand. From this place to Point Keewawoonan, the coast is 

 rocky, but with occasional arenaceous deposits. The predomi- 

 nating rock is red and gray sandstone, of calcareous and ferrugi- 

 nous cement, the nodules being principally of quartz, with a few of 

 hornblende and other rocks. It is usually horizontal, but at 

 Train Isle, it dips to the N.E. Granite seems to occur plentifully 

 from Granite Point westwards : and first shews itself there, to the 

 traveller coming from the Falls of St. Mary. It is described by 

 Mr. Schoolcraft in his sketch of Granite Point : — " A bluff rising 

 out of the lake to the height of 200 feet, connected to the shore 

 by a neck of land, consisting of red and gray sandstone in hori- 

 zontal layers. This granite is made up of red feldspar, quartz, 

 and a little mica, and very much mixed with hornblende. It lies 

 in a confused bed, presenting perpendicular fissures, and traversed 

 by regular veins of greenstone trap. These veins of greenstone 

 vary from two to thirty feet in width, and are disposed to break 



