

190 Dr. BiGSBY on the Geography and Geology of Lake Huron. 



Being- delayed at a point 10 or 12 miles west of the Missassaga^ for thirty-six 

 hourSj I examined the beach of the mainland for one or two miles. 



I here met, protruding from the woods into the lake, a I'ock, which is an 

 intermixture, on a large scale, of a light-coloured greenstone, and a compound 

 of white quartz and red feldspar minutely blended, but the latter predomi- 

 nating-. These two aggregates mutually penetrate and traverse each other in 

 the most capricious forms (as in marbled paper). They are in equal quan- 

 tities ; each being indicated by strongly contrasting configurations, knotty, 

 straight, waved, or stellular. Ramond compares the contortions and con- 

 fused appearances of certain rocks in the Pyrenees, to the effect produced by 

 a mixture of differently coloured glutinous liquors, issuing from separate ves- 

 sels at the same time, or to convolutions of smoke. These comparisons apply 

 well to the masses under consideration *. 



These mounds exhibit no tendency to stratification; but their long diameter 

 appeared to be always directed to the north-west. They are found westward 

 for some miles near the shore, accompanied by a few granitic mounds, holding 

 a northern course. 



The limits of this rock are not known. It is succeeded on the west by the 

 morasses about Thessalon river. It has given the name of Le Serpent to 

 that part of the north shore in which it occurs. Greenstone slate f, lying 

 beneath a granular quartz to be noticed hereafter, is found in one of the 

 islands forming the insular groups north of False Detour. The granular quartz 

 of Green Island is succeeded on the west, after a small interval of marsh, by 

 various greenstones, extending along the north side of the channel and nar- 

 rows of Pelletau. 



At the lower end of the broad promontory constituting the east side of Port- 

 lock Harbour, and in the small isles on its east, the greenstone is dark and 

 compact, but here and there rendered slaty by weathering. It contains, in 

 patches, numerous masses of the red ingredient of the rock of Le Serpent, 

 from one to eighteen inches in diameter ; all bearing positive marks of attri- 

 tion to a moderate degree, and sometimes becoming so plentiful as to make the 

 rock a decided conglomerate. Proceeding still westwards, by degrees the red 

 ingredient disappears altogether, and the greenstone resembles a splintery 

 slate, commonly of a dark leaden hue, which runs hovi ever either rapidly or 

 gradually into cream-colour, red, blue, or light green. Its course is distinctly 



* A somewhat similar rock appears to have been found by Dr. MacCulloch in the Isle of Ar- 

 ran, not far from Glenleg. Vide Western Isles of Scotland^ vol. ii. p. 399. 



f The greenstone slate of the northern shore breaks, often, with a very sharp edge and con- 

 choidal fracture. 



