CHAPTER XXV 



NIAGARA FALLS A CLOCK OF RECENT GEOLOGICAL 



TIME 



Features in and about the Niagara gorge. A striking ex- 

 ample of those permanent alterations of drainage which have 

 resulted from the presence of the late continental glacier in North 

 America is to be found in the Niagara gorge between Lakes Erie 

 and Ontario. With the aid of borings many of the now buried 

 channels of the region have been followed out, and in a later para- 

 graph we shall refer to some of the stronger lines of the earlier 

 drainage system. Before undertaking the study of Niagara his- 

 tory, it is essential that one become somewhat familiar with the 

 present topography in and about the Niagara gorge. 



Below the present cataract the river flows through a deep gorge 

 for about seven miles before issuing at the Lewiston Escarpment 

 (Fig. 381, p. 355). This gorge has been cut in beds of rock sedi- 

 ments which dip at a gentle angle southward toward Lake Erie. 

 The capping of the rock series is a compact and relatively resist- 

 ant limestone which is known as the Niagara limestone, beneath 

 which there are alternating beds of shale with thinner limestone 

 and sandstone. The plain formed by the upper surface of the 

 limestone capping terminates in the Lewiston Escarpment, which 

 is transverse to the direction of the gorge and seven miles distant 

 below the Falls. The depth of the gorge varies markedly, the 

 above-water portion being represented at the upper end by the 

 height of the cataract, one hundred and sixty-five feet, while at 

 its lower end near Lewiston it is twice that amount. Halfway 

 down the gorge a sharp turn is made at an angle of more than 

 ninety degrees, and the upstream arm is extended to form a 

 basin which contains the famous whirlpool. This visible exten- 

 sion of the upper gorge is continued in a buried channel, the St. 

 Davids Gorge, which extends to the escarpment, broadening as 

 it does so in the form of a trumpet. The materials which fill 

 this earlier channel are notably coarse glacial deposits (Fig. 389). 



352 



