No. 4.] CLAYPOLE — PRE-GLACIAL GEOGRAPHY. 197 



Niagara, probably forming a series of Rapids into the Ontarian 

 plain. After traversing this from west to east, it escaped through 

 the buried channel at Oswego, which it followed along the 

 course of the present Mohawk until it reached the Hudson, then 

 perhaps the smaller stream, and both united entered the Atlantic 

 at some point south-east of where New York now stands. 



One other point deserves a passing notice, but, for want of 

 exact knowledge, it can only be at present an indication of pro- 

 bability. A striking feature in the geology of Canada is the 

 great Silurian escarpment, as it is called. It consists of a range 

 of cliffs, in some places two or three hundred feet high, com- 

 mencing on the west bank of the Hudson, and forming the 

 southern boundary of the valley of the Mohawk. Thence ex- 

 tending nearly due west to Niagara it sweeps round the western 

 end of Lake Ontario to Cabot's Head, the Manitoulin Isles and 

 Mackinaw, and skirts the western shore of Lake Michigan.* 



This escarpment faces the north, and forms, at present, an 

 imperfect division between Lake Huron and the Georgian vale. 

 But when elevated, as in the later Tertiary age, it must have 

 formed a water-shed between the Huronian valley and that in 

 which now lie the waters of the Georgian Bay ; and the question 

 arises, in what direction did the waters of the Georgian valley 

 then flow ? A study of the geography of the country leads to 

 the suspicion that they may have found their way to the east- 

 ward by the valleys of the present Severn and Trent and the 

 Bay of Quinte. Sir William Logan, writing on this subject in 

 the Geology of Canada, 1863, pp. 12, 13, describes a ridge of 

 drift material running nearly east and west, at a short distance 

 from Lake Ontario, and dividing the Lake Basin from the val- 

 ley of the Trent or Ottonnabee. " Between the Holland and the 

 Humber, Mr. Tully in his report on the proposed Georgian Bay 

 canal, states the height of the ridge to be 904 feet above the 

 sea. To the east of this it is crossed by the Toronto and Simcoe 



* It appears as if geologists who advocate the excavation of the 

 basins of the great lakes by the action ot northern ice flowing off the 

 Laurentian highlands, are somewhat oblivious of the existence of this 

 escarpment. If the ice possessed the enormous eroding power on 

 rocks and cliffs so often attributed to it, it must certainly have cut 

 away and destroyed this gigantic barrier to its advance before pro- 

 ceeding to scoop out deep basins to the southward. 



