ST. LAWRENCE BASIN — GEOLOGICAL STRUCTURE. 185 



ridge formed by these rocks does not exceed the height 

 of 700 feet above the river or lake surface ; but, par- 

 taking of the general eastern slope of the continent, it 

 attains a height of about 1,400 feet above the sea on the 

 north side of Lake Superior. * The course of the St. Law- 

 rence through Canada East is conformable to the general 

 strike of the beds in which the channel is excavated. 



The geological structure of the north side of the St. 

 Lawrence basin, as ascertained by the Canadian state 

 survey under Mr. Logan, has been summed up as follows 

 by his assistant, Mr. Hunt : — "A formation of syenitic 

 gneiss, often passing into mica- schist, and interstratified 

 with crystalline limestone, forms a ridge of high land ex- 

 tending from the coast of Labrador along the north side 

 of the St. Lawrence, at a distance of from twelve to twenty 

 miles from the shore, until it crosses the Ottawa, near 

 Bytown, and thence is traced across Lake Simcoe to the 

 shores of Lake Huron, where its northern limit is observed 

 near the mouth of the French River, while it again ap- 

 pears at the south-eastern extremity of the lake in Matche- 

 dash Bay. Besting upon this is a series of rocks forming 

 the whole north coast of the lake, and numerous small 

 islands. It is made up of sandstones, often coarse-grained, 

 and sometimes becoming conglomerate from the presence 

 of red jasper pebbles. These beds are associated with 

 slates and one or more bands of limestone. . . . The 



* The following ascertained points may be noticed : — Lake Tem- 

 iscaming, which is high up on the Ottawa, and near the line dividing 

 the water-shed of that river from the Abitibbe and Moose River, 

 which falls into Hudson's Bay, was ascertained by Mr. Logan to be 

 612 feet above the tide. The dividing portage between the Ottawa 

 and Lake Nipissing is 696 feet above the sea, the lake itself being, 

 according to Mr. Murray, 647 feet high. Lake Simcoe was ascer- 

 tained, by the same observer, to have an altitude of 704 feet above 

 the tide. — Logans Geol. Rep. for 1848. 



