GEOLOGICAL AREAS OF CANADA. 15 



marl, (fee. The Drift or Glacial gravels form a series of roughly 

 parallel terraces or ridges, running from the Niagara escarpment, or 

 its vicinity, in a general west and east direction. The highest ridge 

 is in places from 700 to 750 feet above Lake Ontario. The latter is 

 232 feet above the sea. 



(4.) The Erie and Htiron District. — Forms a comparatively 

 elevated table-land, extending froin the summit of the Niagara 

 escarpment southwards to the Niagara River and Lake Erie, and 

 westward to Lake Huron. In its central and north-easteiii portions 

 it presents an average elevation of from 1,000 to 1,200 feet (higher 

 in places), but slopes gradually to Lake Erie, 565 feet, and to Lake 

 Huron, 578 feet above the sea. Constitutes a very fertile agricul- 

 tural region, underlaid by Middle and Upper Silurian, and succeeding 

 Devonian formations : the more important comprising the Clifton, 

 Niagara, Guelph, Onondaga, Corniferous, and Hamilton subdivisions. 

 The district is apparently traversed by some flat anticlinals running 

 in a general west and east, or north-east, direction, but its strata are 

 otherwise practically undisturbed. Gypsum deposits occur largely 

 in the Onondaga strata ; and brine and petroleum are obtained, by 

 boring, from the Devonian formations. Glacial, Post-Glacial, and 

 Recent accumulations, overlie the district generally. 



(5.) The Manitoulin District. — Comprises the Great Manitoulin 

 and adjacent series of islands lying off the north shore of Lake 

 Huron. Geologically, it foi-ms a continuation of the Ontario and 

 Erie Districts, being underlaid essentially by Siluiian strata, striking 

 nearly due east and west, and following each other in ascending 

 order from north to south. The principal subdivisions comprise the 

 Black River-and-Trenton, Utica, Hudson River, Mediiia-and-Clinton, 

 Niagara, and Guelph formations. In the Great Manitoulin, the 

 northern portion contains numerous lakes, and the north coast is 

 indented by deep bays, originating, aj)parently, in anticlinal undu- 

 lations. The Niagara escarpment, with its steep face towards the 

 north, runs throxigh the entire island ; and, southwards, bare out- 

 crops of flat limestone strata extend over many acres. In other 

 places the rocks are mostly covered by Glacial and Post-Glacial 

 deposits, yielding tracts of average fertility. 



(6.) The District of the Upper Lakes. — This district comprises a 

 vast area of a more or less mountainous character, extending, from 

 the north shores of Lake Huron and Lake Superior, to the boun- 

 daries of the Province in the north and west. It is essentially a 



