40 



Sarnia is 1,248 feet (379.4 m.), while in the county of Grey 

 near Collingwood a maximum elevation of 1,706 feet 

 (518.6 m.) is reached in the Blue mountains. 



A heavy mantle of drift covers almost the whole of 

 the area and, in places, attains a remarkable thickness. 

 Post-glacial accumulations in the form of stratified sands 

 and clays are widely distributed and the strand lines of 

 post-glacial lakes are marked by beaches of gravel and 

 sand. These glacial and post-glacial soils are of great 

 fertility and, aided by the southerly latitude, render the 

 Western Peninsula of Ontario one of the finest agricultural 

 sections of Canada. 



Glacial striae with a general southwest trend are to be 

 seen wherever the rock is sufficiently hard to retain them 

 and the exposure to the weather has not been too long. 



The rock basin of Lake Ontario, at its deepest point, 

 is 738 feet (224.4 m -) beneath the surface of the lake, and 

 Lake Huron reaches a maximum depth of 750 feet (228.0 

 m.). On the other hand, Lake Erie is nowhere more than 

 210 feet (64.0 m.) deep, and its average depth is very much 

 less. The deepest part of Lake Ontario is off its southern 

 shore: this lineal depression is thought to represent the 

 bed of a great pre-glacial river which entered the basin of 

 Lake Ontario from the west and drained a wide area in 

 that direction. The waters of the Lake Huron basin are 

 believed to have entered the Ontario valley by a great 

 river whose course was down the western side of Georgian 

 bay, across the Province of Ontario to a point a little east 

 of Toronto and thence southward to a junction with the 

 river in the Ontario basin. It would appear, therefore, 

 that in pre-glacial times, Lake Erie did not exist and that 

 Lakes Huron and Ontario were either absent or of much 

 restricted area. 



The enormous accumulations of drift which choked the 

 above mentioned pre-glacial valleys are responsible, with 

 some later modifications, for the present distribution of 

 land and water in this area. Significant of the recent 

 origin of the present system of drainage, is the fact that the 

 water of streams rising 25 miles (40.0 km.) north of Toronto 

 follows a circuitous path of 700 miles (1126-5 km.) in order 

 to gain access to Lake Ontario. The thousands of islands 

 along the eastern side of Georgian bay likewise attest the 

 recent invasion of the waters of Lake Huron into the Pre- 

 Cambrian oldland of Central Ontario. 



