NIAGARA FALLS AND VICINITY 



49 



the preglacial divide has an elevation of 440 feet above sealevel. 1 

 The following diagram (fig. 8) shows the present relation of the 

 deepest part of the channel of Lake Ontario to sealevel, and the 

 relation which would result by a tilting of the land back to its 

 probable position in preglacial times. The last profile shows a con- 

 tinuous westward slope of the floor of the valley, steeper in the 

 eastern portion, where the rocks are harder and the valley narrower, 

 and more gentle in the western portion, where the softer rocks have 

 allowed the opening of a broad lowland. 



Fig. S Diagram showing the present deepest e-w channel of Lake Ontario along line 1-1, and its re- 

 lation to sealevel s. 1. and the level of Lake Ontario 1. o. At 1, leftside of diagram is represented the 

 bottom of the channel at Vienna, 200 ft below level of Lake Erie or 370 ft above sealevel. At 1, 

 right side, is the divide at Littlefalls 440 ft A. T. The line 1-2, is the line 1-1, but elevated on the 

 east (right) so as to give a continuous westward drainage. Horizontal scale 1 inch = 100 miles. Ver- 

 tical scale 1 inch = 4000 feet. 



Numerous theories have been advanced to account for the deep 

 basin of Lake Ontario. Spencer believed it to have been formed by 

 an eastward flowing stream, the ancient Laurentian river, which re- 

 ceived the Erian river as a tributary through the Dundas valley. 

 The eastward continuation of this river Spencer believed to have 

 been essentially along the course of the modern St Lawrence, the 

 present great elevation of the rocky bed of this stream, above that 

 of Lake Ontario, being explained by a warping of the land. Up- 

 ham also believes that the basin is in part due to warping, but he 

 considers it the valley of a westward flowing stream. Russell also 

 holds this latter view; for he says 2 that, "previous to the glacial 

 epoch, the greater part of the Laurentian basin discharged its 

 waters southward to the Mississippi and . . . during the first 

 advance of the ice from the north the drainage was not obstructed 

 so as to form important lakes ". Westgate 3 , in tracing out the de- 



x Bigelow. Bui. geol. soc. Am. 9:183. 

 2 Lakes of North America, p. 97. 

 z Loc. cit. p. 92. 



