in the Lake Ontario basin were drawn down to a level some- 

 what lower than the present level of Lake Erie. This 

 inaugurated the flow of Niagara river and completed 

 the separation of Lake Erie from Lake Ontario. Niagara 

 Falls then began the work of making the gorge at the escarp- 

 ment south of Lewiston. 



PHYSIOGRAPHIC DEVELOPMENT. 



Niagara district lies between Lake Erie and Lake 

 Ontario, in the midst of a region which has the physio- 

 graphic and geologic characteristics of an eroded, ancient 

 coastal plain. Following the deposition of the Paleozoic 

 sediments, the region as a whole was raised out of the 

 sea about at the close of the Paleozoic era and appears 

 to have been a land surface ever since. In so great a 

 length of time the region has, of course, been extensively 

 modified by subaerial and stream erosion, but it does 

 not appear to have been affected by marine denudation. 

 The highlands of Canada are the oldland, and the beds 

 of the ancient coastal plain dip gently southward from it. 

 Some of these beds are soft and others hard, and in con- 

 sequence of this difference the softer beds have been 

 reduced, to lowlands, while the harder beds remain as 

 uplands of relatively low relief. Thus, through the 

 effects of erosion, the ancient coastal plain has become 

 a belted plain composed of a series of narrow, nearly 

 flat plains separated by northward facing escarpments, 

 like a flight of steps descending to the north. But the 

 tread of each step slants gently backward towards the 

 south and produces the form which in New Mexico is 

 called a cuesta, meaning a low ridge, steep on one side, 

 but with a gentle slope on the other. 



South of the oldland lies the Ontario lowland, and the 

 basins of Lake Ontario and of Georgian bay are excavated 

 in it. To the south of this lies the Niagara cuesta with 

 its strongly marked escarpment facing northward over the 

 Ontario lowland and Lake Ontario. South of Lake Erie 

 and extending eastward through New York lies the Alleg- 

 hany cuesta. It has been customary in the small scale 

 maps usually employed, to recognize only one simple 

 lowland as occupying the whole space between the Niagara 

 and Alleghany cuestas, and this has been called the Erie 

 lowland. But when the region around Niagara is studied 



