422 LAKE SUPERIOR. 



r 



everywhere along these shores, coves, deep coves, narrow, straight 

 inlets, small caves, and gives to the whole extent of that shore that 

 peculiar aspect which distinguishes it so much from the other parts 

 of the lake. 



The more precipitous shores almost vertical walls, and those pe- 

 culiar modes of decomposition of the rocks which have left strange 

 appearances in the masses, some of which have even been noticed 

 by the Indian voyageurs, as Otter Head, for instance the number- 

 less exceedingly small islands of these shores, and the striking bald* 

 ness of the overhanging rocks, are all of them most remarkable 

 features. Though these examples are very striking, and may at 

 once satisfy the mind that the most minute details in the peculiar 

 features of the lake may be ascribed to geological agency, we never- 

 theless find still more striking evidence of this connection between 

 the geological structure of the country and its form, along the north- 

 western shore, west of St. Ignace, and between Isle Royale and 

 Fort William. Three other systems of dykes here intersect the 

 rocks, and give to the whole shore an entirely different aspect. At 

 first sight, the bearings of the north-westerly shore appear already 

 different from those of the northern shore proper, and the eastern 

 shore, as their general course is north-east and south-west from the 

 southern extremity of St. Ignace to Pigeon Bay, to which Isle Roy- 

 ale is parallel. But upon a close examination of these shores, it 

 becomes obvious that this general feature is modified in various ways 

 by the lines of the shore intersecting each other at acute angles, in 

 three directions, and each of these different directions correspond 

 exactly to as many systems of independent dykes. The eastern and 

 western shores of Thunder Bay, or rather of the peninsula of Thun- 

 der Cape, run north-east, and parallel to them we have the cliffs of the 

 shores south of Fort William, and west of Pic Island, which present 

 the same bearings, as well as the shores of Black Bay also. The 

 dykes which run in that direction are narrow belts of black trap. 

 Nearly in the same direction, and very different in their mineralogi- 

 cal character, we find another set of dykes which run almost due 

 north-east and south-west. The direction of these dykes is best indi- 

 cated by a series of islands south of Sturgeon Bay, forming several 

 parallel ridges, one of which consists of a series of small islands 



