164 Transactions of the Canadian Institute. [Vol. VII. 



The northeastward extension of the Ontario lowland merges gradu- 

 ally with the CLiesta formed by the Black River strata. The escarp- 

 ment-front of the Black River cuesta extends from the vicinity of 

 Kingston northwestward to Georgian Bay, and thence across the ba}-, 

 beneath whose waters it seems to be still traceable, to the Manitoulin 

 Islands. The unsubmerged portion of the escarpment averages about 

 ninety feet in height, and locally is occasionally much higher. In the 

 region west of Lake Simcoe, and in northern parts of Hastings and 

 Addington counties, it is partly obscured by drift deposits. 



The fronts of both cuestas present many irregularities appropriate to 

 development under subaerial processes. The principal physical features 

 of " Old " Ontario are those characteristic of an ancient coastal plain 

 which has passed through a period of planation followed by one of 

 uplift, dissection, and the development of an adjusted drainage system. 

 Similar topographic forms have been developed, also with var}-ing 

 strength and expression, in Middle England, in the Paris Basin and 

 elsewhere near old land areas. 



The drift deposits in Central Ontario form a prominent ridge, or 

 series of ridges, the Oak Ridges, of varying breadth, lying at an average 

 distance of about ten miles north of Lake Ontario, and extending east- 

 ward to the vicinity of Trenton. At the western end, near Palgrave, 

 the thickness of the deposits is sufficient to almost obliterate the escarp- 

 ment of the Niagara cuesta. A number of spurs extend southward and 

 northward from the main ridge. 



This morainic ridge divides Central Ontario into two drainage slopes, 

 a northern and a southern. The Trent river, the largest stream within 

 the area, conveys a large percentage of the drainage from the northern 

 slope, and from the southern slopes of the crystalline area to the north, 

 across the ridge to the Bay of Ouinte in the vicinity of Trenton. The 

 remaining portion of the drainage of this northern slope reaches 

 Georgian Bay, chiefly by the Severn river from Lake Simcoe basin, and 

 by the Nottawasaga river. The waters from the southern drainage 

 slope reach Lake Ontario by a number of small streams. East of 

 Trenton the drainage, which is across the area from within the Black 

 River cuesta, is controlled almost wholly by the rock topography. 



The present features of Central Ontario, as a product of the 

 operation of the two processes, Pliocene and early Pleistocene subaerial 

 erosion, and Pleistocene erosion by sheet-glacier ice, are of special 

 interest, not only in themselves, but because of their relation to the 



