NIAGARA FALLS AND VICINITY 



69 



worn away by the spray generated by the faUing water, thus under- 

 mining the resistant layer. Such undermining may be seen in the 

 Cave of the Winds. In course of time this undermining progresses 

 so far that the projecting portion of the capping stratum breaks 

 down for want of support, and the crest hne of the fall becomes 

 abruptly altered. The fallen fragments accumulate at the foot of 

 the fall, where they will remain if the force of the water is unable 

 to move them, as illustrated by the rock masses lying at the foot 

 of the American fall. If, however, the force of the falling water is 

 great as at the Horseshoe falls, these blocks will be moved about, 

 perhaps even spun about, and so made to dig a deep channel below 

 the falls. In the soft rocks which lie at the foot of the Horseshoe 

 falls a channel probably not less than 200 feet in depth has been 

 dug in this manner. (Fig. 15) 



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1'.' '^--s% 



■1' r 



V I- M 





Fig. 15 Sectional view of the Horseshoe falls showing ari-angement of strata, and depth of water 

 below falls. (After Gilbert) The numbering of beds corresponds with that of table. 



When we consider the Niagara gorge in detail we find it to be 

 much more complex than would at first appear. The first ab- 

 normal feature which presents itself in a map view of the entire 

 gorge is the bi-crescentic character of its course, with the rectan- 

 gular turn at the whirlpool, a course very different from that which 

 we are accustomed to find in large rivers whose direction of flow 



