360 EARTH FEATURES AND THEIR MEANING 



must have been constantly weakened as its thickness was further 

 reduced. 



When this weakened dam at last gave way, it must have pro- 

 duced a debacle grand in the extreme. It is hardly to be conceived 

 that the " washout " of the ancient channel to form the Whirl- 

 pool Basin could have occupied more than a small fraction of a 

 day, though it is highly probable that the broken rock partition 

 below the Whirlpool was not immediately removed entire. The 

 manible-like termination of the Eddy Basin immediately above 

 the Whirlpool has led Taylor to believe that the cataract quickly 

 reestablished itself at this point upon the last site of the extinct 

 St. Davids cataract. If reduced in power for a short interval, as a 

 result of the obstructions still remaining in the lately broken dam 

 below the Whirlpool, the remarkable narrowing of the gorge at 

 this point would be sufficiently accounted for. 



Being compelled to turn through more than a right angle after 

 it enters the Whirlpool Basin, the swift current of the Niagara 

 River is forced to double upon itself against the opposite bank 

 and dive below the incoming current before emerging into the 

 Cove section below the Whirlpool (Fig. 386). 



In tearing out the loose. deposits which had filled this part of 



the buried St. Davids Gorge, 

 many bowlders of great size 

 were left which slid down the 

 slope and in time produced an 

 armor about the looser deposits 

 beneath, so as to protect them 

 and prevent continued excava- 

 tion. Thus it is found that the 

 submerged northwestern wall 

 of the basin is sheathed with 

 bowlders large enough to retain 



the Niagara Gorge, and the drift bank natural process of placer Ollt- 

 which forms the northwest wall (after washing Upon a gigantic scale 



(Fig. 386). 



The shaping of the Lewiston Escarpment. To understand 

 the formation of the Lewiston Escarpment cut in the hard Niagara 

 limestone, it is necessary to consider the geology of a much larger 



