586 AN OUTLINE OF THE GEOLOGY OP ONTARIO, 



underlaid essentially by hard crystalline rocks, belonging, for tlie 

 greater part to the Laurentian sei-ies. The surface of Lake Huron 

 is 578 feet, and that of Lake Superior 600 feet above the sea. From 

 these levels the ground rises more or less abruptly to an average 

 height of from 1,000 to 1,500 feet, with occasional points of still 

 greater elevation. The recognized rock formations comprise repre- 

 sentatives of the Laurentian, Huronian, Upper Copper-bearing, and 

 Chazy C?) series, with many eruptive granitic and trappean rocks, and 

 overlying Glacial and post-Glacial deposits. 



The Laurentian rocks are composed of vast beds of micaceous and 

 hornblendic gneiss, quartzites and other crystalline strata ; but the 

 bands of crystalline limestone associated with these rocks in eastern 

 districts are here apparently wanting. These Laurentian strata are 

 mostly inclined at high angles, and are variously folded and contorted 

 by undulations. In places also they are broken through by vast 

 masses of granite. They form a great part of the north and east 

 coasts of Lake Superior ; but along the north shore of Lake Huron 

 they are mostly overlaid by Huronian strata, although forming the 

 coast-line from the River Thessalon to a short distance east of the Mis- 

 sissagui. In the back country of both lakes, however, they extend 

 over almost the entire surface of the region. 



The Huronian strata are composed mostly of gi-een and other 

 slates, quartzites, quartz and jasper conglomerates, and other rocks, 

 for the greater part of semi-crystalline aspect. They are interstra- 

 tified also with trappean bands, and are penetrated by numerous 

 dj^kes of trap and greenstone. In many places likewise they are 

 traversed by quartz veins carrying ores of copper and other metals. 

 They form a broad belt ranging from Lake Temiscamang to Lake 

 Huron, west of French River, and along the lake shore to the River 

 Mississagui. They reappear again on the coast west of Thessalon 

 River, and occupy a large area between Lake George and the country 

 around Echo Lake. They occur also on the east and north- west coast 

 of Lake Superior, and in a band at the back of Thunder Bay, as well 

 as in several other bands farther west and north, where they appear, 

 according to Prof Robert Bell, to occupy synclinals, in folds of Lau- 

 rentian strata. Their more important economic minerals comprise ; 

 the copper ores of Lake Huron (Bruce Mines, etc.) ; the iron ores of 

 Echo Lake, Michipicoten River, Pic River, etc^; the antimony ore of 

 Echo Lake country; the silver bearing veins (3 A mine, etc.) of the 



