AN OUTLINE OP THE GEOLOGY OF ONTARIO. 585 



ring, as already described, in. the Lake Ontario region. The more 

 important economic minerals of the district comprise, in addition to 

 petroleum, the gypsum of the G-rand River valley, etc.; the hydraulic 

 limestone of Thorold ; the brine of the Goderich region ; the ochres 

 of Middlesex and Norfolk ; and the peat beds of Humberstone and 

 Wainfleet on Lake Erie. 



The Manitoulin district partakes of the characters of both the On- 

 tario and Erie districts, as the Silurian strata of these latter range 

 entirely through it. The district comprises the Great Manitoulin 

 Island, eighty miles in length, with the La Cloche and other smaller 

 islands lying between it and the mainland, and Cockburn Island, 

 Campement d'Ours, St. Joseph's Island, etc., farther west. Drum- 

 mond Island belongs also geologically to the district, but lies beyond 

 the Dominion boundary. The strata of the district succeed each other 

 in passing from north to south, the general dip being in the latter 

 direction. They comprise a slight development of Huronian quart- 

 zites, with representatives of the Chazy (i), Trenton (including the 

 Black River beds), Utica, Hudson River, Medina and Clinton, Nia- 

 gara and Guelph formations. The Niagara escarpment runs from 

 east to west through the Great Manitoulin Island in the form of a 

 cliff face, fronting northwards, and the southern half of the islaod is 

 composed essentially of limestone beds of the Niagara formation, 

 bare outcrops of these rocks forming in many places " the surface of 

 the ground. Northwards, the arenaceous shales of the Hudson River 

 series, with outlying band of Utica slate, and fringe of Trenton lime- 

 stone, are the more characteristic formations. The north part of the 

 island contains numerous lakes, and its north shore is indented by 

 comparatively deep bays. These and the lakes appear to lie in syn- 

 clinal folds, formed by a series of anticlinals, with north and south 

 axes, which traverse the island throughout its length. The rocks of 

 the district generally are marked with glacial striae, and northern 

 boulders are abundant in many localities. Petroleum springs occur 

 on the Great Manitoulin, in the Utica formation, but wells sunk upon 

 these have yielded no permanent supply of any importance. 



The district of the Upper Lakes may be defined in general terms 

 as extending over the entire north-western portion of Ontario, from 

 Lake Tamiscamang and French River, on Lake Huron, to the boun- 

 dary of the Province beyond Lake Superior. It forms a rugged, 

 mountainous region, broken up by numerous bodies of water, and 



