﻿1851.] 



BIGSBY ON CANADIAN ERRATICS. 



225 



shivered and disintegrated by alternate thaw and frost, that it is not 

 easy without tools to get at the rock below. 



This state of things is somewhat unusual in Lake Huron, for the 

 primitive rocks are ordinarily sound, often highly polished and 

 rounded like woolsacks. 



In these narrows, which are about a mile wide, we see that each 

 shore is lined exclusively with its own debris. 



The loose masses on the north side of Lake Huron belong in the 

 greater proportion to the immediate vicinity ; but these vary greatly as 

 we pass from Point Thessalon to Penetanguishene, about 280 miles. 



Between the rivers Thessalon and Missassaga, and especially thir- 

 teen miles east of the former, the beach is so encumbered with erratic 

 boulders as to impede landing. They are granites, traps, and gneiss, 

 with a quantity of the jasper-pudding-stone, so much admired by all 

 who have seen it*. Black trap seemed to form the most abundant 

 boulder. I saw no loose limestone on the main shores west of the 

 river Missassaga. It was here that I was puzzled by the almost 

 constant scorings and striae (unconnected with the stratification), by 

 the polished and glazed surfaces, and the woolpack forms of the rocks 

 around, — appearances precisely similar to what I afterwards saw in 

 Switzerland and in North Wales, but which in 1824 I was quite un- 

 able to interpret. 



Eleven miles east of this river the main shore and its beach are 

 remarkably infested with large blocks. On a syenite island in the 

 offing here, one of a nameless group, quartz-rock, rendered slaty by 

 the presence of mica, is introduced largely among the traps, granites, 

 and jasper-pudding-stones, and so continues through the Le Serpent 

 district on the east. The micaceous rock comes from the hills of the 

 mainland at La Cloche, where I have seen it. 



As we approach the La Cloche district, and pass through its groups 

 of isles and winding sheets of water, as far as Collin's Inlet, square 

 masses (5-20 lbs. weight) of sparkling, fine-grained quartz, line almost 

 every shore nearly to the exclusion of all other rocks, except now and 

 then slabs of Trenton limestone, loose or in place, full of fossils. In 

 Collin's Inlet these quartz-rocks are rolled ; elsewhere they do not 

 present that appearance in nearly so great a degree. 



The quartz-rock prevails in a fixed state for many miles around, 

 and is traversed by dykes of trap. One very large black block of 

 trap was shown me on the mainland as having given the district its 

 name, from its ringing loudly on being struck. 



Proceeding eastwards, on and around the Fox Islands, opposite 

 Collin's Inlet, thirteen miles west of the French River, the boulders 

 of jasper-pudding-stone re-occur, with much greenstone, porphyry, 



* I saw here a cubic block of 4 feet every way. It has been described by 

 Logan and others. I saw this description of debris in situ on the adjacent shore, 

 as well as on the Isle of Encampment Doux (not D'Ours) at the East Nibish 

 Rapid, where the white crystalline quartz-rock is striped by bands (1-5 feet broad) 

 of red, brown, and green jasper nodules. Mr. Logan also found it in great mass 

 in a small lake three miles from Lake Huron, near Portlock Harbour, and on Thes- 

 salon Lake, some miles to the east. 



