198 THE CANADIAN NATURALIST. [Yol. viii. 



railroad, while to the west where it abuts against the Upper 

 Silurian escarpment, and separates the Humber from the Notta- 

 wasaga, its height is 950 feet." 



" Lake Simcoe is a tributary to Lake Huron, and lies 704 

 feet above the sea, but the depression in which it is situated is a 

 continuation of the valley of the Trent, which can thus be traced 

 from the Georgian Bay to Kingston." 



" If the palaeozoic rock surface beneath the drift ridge pre- 

 sents the same character as it does in other parts of the plain, 

 it seems probable that it rises with a pretty even slope from the 

 exposures on the lake to those north of it in the latitude of 

 Peterborough, and that a depression accompanies the softer de- 

 posits from the Georgian Bay to Lake Ontario. This would 

 give a probable depth of 400 feet to the drift along the chief 

 part of the ridge, and a still greater depth over the depression." 



Now Lake Simcoe, lying 704 feet above the sea, is only 130 

 feet above the level of Lake Huron, and if, as Sir Wm. Logan 

 supposes, the rock lies more than 400 feet below the surface, it 

 is evident that before the deposition of the drift, the waters of 

 the Georgian valley may have flowed eastward along the depres- 

 sion where now lies the chain of Lakes Simcoe, Balsam, Cameron , 

 Sturgeon, Mud, Salmon Trout, and Bice, and the present river 

 Trent into the Bay of Quinte, at the eastern end of which they 

 may have entered the Ontarian valley, and the pre-glacial Otton- 

 nabee may have been a tributary of the pre-glacial Mohawk. 



These are some of the changes which the elevation of the 

 northern part of the continent before the deposition of the drift, 

 probably implied, bnt we can trace them somewhat further. 

 Three-fifths of the great system of fresh water lakes have already 

 disappeared from our Tertiary geography, and it is evident that 

 the same elevation will efface the most beautiful river of the 

 continent, the St. Lawrence. 



The St. Lawrence, at Quebec, is much farther to the north 

 than Lake Ontario. The elevation due to its latitude, at the 

 same rate as before, must have placed it at the time in question 

 about 1300 feet above the Atlantic, while Montreal and Kingston 

 were nearly 1000 feet above the same level. Instead therefore 

 of flowing to^ the north-east the drainage of the waters of the 

 district must have taken a south-westerly direction, and in all 

 probability passed by some channel across the great plain be- 

 tween the St. Lawrence and the Green Mountains, not far it 



