A CLOCK OF RECENT GEOLOGICAL TIME 



353 



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Directly above the whirlpool the Niagara gorge is first con- 

 tracted, but almost immediately swells out into the form of a 

 sausage, which under the name of the Eddy Basin extends to the 

 constricted channel occupied by the Whirlpool Rapids. This Gorge 

 of the Whirlpool Rapids extends to and a little above the railroad 

 bridges, where it again suddenly widens and deepens and with 

 surprisingly uniform cross section now continues as far as the cat- 

 aract. This uppermost section is known as the Upper Great 

 Gorge. About a mile below the whirl- 

 pool is that remarkable projection into 

 the gorge from the Canadian wall which 

 is known as Wintergreen Flats, below 

 which and nearer the river are Fosters 

 Flats. Almost throughout its entire 

 length the Niagara gorge is bordered 

 on either side by a narrow and gently 

 incurving terrace eroded below the gen- FIG. 377. ideal cross section 

 eral level of the plain and meeting the of the Niagara gorge to show 

 gorge in a sharp angle (Fig. 377). 



The features immediately about the cataract show that the Falls 

 are to-day in a condition which, so far as we know, has occurred 

 but once before in their entire history the waters of the river 

 are divided unequally by an island, and for this reason, as we shall 

 see, the cataract enters over the side wall of the gorge instead of 

 at its end (Fig. 381), although the turning of the channel from this 

 cause is combined with a bend of the river. 



The drilling of the gorge. There appear to be two important 



processes which are responsible 

 for the recession of the Falls, 

 the rate of which is determined 

 largely by the resistance of the 

 limestone capping and the tena- 

 city of the looser shale beneath 

 it. One of the eroding processes 

 FIG. 378. - view of the bed of the Niagara operates from below and under- 



River above the cataract, where water mines the Cap Until the Unsup- 



has been drained off in installing a power p Or t e d Cornice falls in blocks 



plant. Some separated blocks of lime- . - , , 



stone are still in place (after J. W. to the bottom f the 8 or 8 e J 



Spencer). the other makes its attack di- 



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