54 NEW YORK STATE MUSEUM 



cient Dundas river. Throughout western Ontario this escarpment 

 is buried by drift, but its presence is indicated by borings, which 

 also prove the continuance of the lowland accompanying it. This 

 escarpment, the inface of the second cuesta, becomes a very promi- 

 nent feature in Lake Huron, where it is entirely submerged. It is 

 however perfectly traceable from north of Goderich in Canada to 

 the island of Mackinaw. Soundings prove it to have a hight of 

 from 350 to 500 feet or more above the lowland which it faces. This 

 lowland constitutes the deeper portions of Lake Huron, the shal- 

 lower southwestern area being a part of the upland drowned by the 

 backward setting of the water over the top of the escarpment. The 

 following cross-section (fig. 9) from Point au Sable, north of 

 Saginaw bay, to Cape Hurd, the northern extremity of the Indian 

 peninsula, passes across the highest portion of this escarpment at 

 the 9 fathom ledge and diagonally across the deepest portion of the 

 Huron lowland, where the soundings reach a depth of 750 feet. 

 This apparently marks the location of the preglacial Saginaw river, 

 which probably breached the second cuesta to the south of the 9 

 fathom ledge, though no channel is indicated by the soundings. 



t^^^xx^ 1 |. 



Fig. 9 Section across Lake Huron from Point au Sable, a) across 9 fathom ledge, b) to Cape Hurd, 

 c) (For location of section see fig. 6). 



We have now traced the development of the topographic features 

 of the Niagara district, and have found this to be in conformity with 

 the laws governing the normal development of drainage systems on 

 an ancient coastal plain. The only abnormal features which need 

 to be considered now are the tilting of the land and the filling of 

 most of the old channels by drift, converting the lowlands into lake 

 basins and reversing the drainage of the unfilled channels. These 

 were the catastrophes which immediately preceded the birth of 

 Niagara and which were directly responsible for its existence. To 

 these and the life history of Niagara, attention will now be invited. 



