Geological Society. 219 



conglomerate rests upon gneiss and other primitive rocks ; but at 

 Malbay it is interstratified with brown limestone, and contains spiral 

 univalves and various bivalves*. The author is inclined to refer 

 the formation to the old red sandstone. 



Theporphyries of Gros Cap and'Nipigeon on Laive Superior, contain 

 agate, chalcedony, fluor, green earth, and vitreous felspar : they are 

 unstratified, and form serrated precipices. Near Gravel Point they 

 much resemble some of the porphyries of Arran in Scotland. 



The rocks of the St. Lawrence Valley, beneath the series above 

 mentioned, consist, in a descending order, of grauwacke, interme- 

 diary limestone, quartz-rock, primitive limestone, and various slaty 

 rocks, — including gneiss, mica slate, actinohte slate, with syenite, 

 greenstone, and ophicalcic rock. The prevailing direction of the 

 strata, for more than 1000 miles, from the River Saguenai, on the 

 north of the St. Lawrence, to the northern shore of Lake Huron, is 

 to the N.E. ; and the rocks are regarded by the author as the most 

 recent of the primitive class. Quartz-rock prevails on the north of 

 Lake Huron for more than 70 miles ; and the islands in that part of 

 the lake consist of fine-grained red and gray granite, with quartz-rock 

 and trap : and vast masses of granite alternate with greenstone for a 

 space of 300 miles on the north shore of Lake Superior. Of the 

 slaty primitive rocks, the most abundant is gneiss ; which constitutes 

 some of the principal heights, and forms the mountains N.E. of Que- 

 bec, and lines the northern shore of the St. Lawrence. Cape Tour- 

 ment, 1800 feet in height, consists of this rock ; so also the outlet of 

 Lake Ontario, and it skirts the north shore of Lakes Simcoe and 

 Huron, and occupies a considerable tract on the north of Lake 

 Nipissing, and at the upper part of the river Ottawa. 



The author supposes that the numerous boulders of Labrador fel- 

 spar on the shores of Lake Huron, on the S. W. of Lake Simcoe, and 

 even so far eastward as the outlet of Lake Ontario, have been de- 

 rived from a tract about GO miles west of Penetanegeneshene, where 

 the gneiss passes into Labrador felspar, traversed by veins of pyroxene 

 and garnet ; and this he supposes to be the southern verge of a vast 

 tract of the same composition. Magnetic iron ore is associated with 

 syenite on the north of Ontario. Greenstone occursin veins in Lower 

 Canada: near Lake Huron it supports intermediary limestone; and 

 it is found at Gros Cap in Lake Superior, and forms numerous dykes 

 of great size in the north shore of that lake. A mass composed of 

 a mixture of augite and hornblende occurs near Montreal, con- 

 stituting Montreal Hill, 6.50 feet high, from which numerous dykes 

 cut through the shelly deposits at the base of the hill. 



The primitive limestone appears in every part of the St. Lawrence 

 Valley to belong to one and the same epoch, and occupies a conside- 

 rablespaceon the south-western frontierof Lower Canada, near Lake 

 Champlain. In Upper Canada, the upper part of the river Ottawa 

 lias its course through this rock, and considerable masses of it oc- 

 cur in Crew Lake : the same white marble is seen at Lake Chat, and 



» Some of the fossils of this formation have been figured in the Guolo- 

 fjiciil Transactions, iiJnd Series, Vol. I. 



2 1" 2 on 



