Niagara Falls 



1880 attack, the limestone capping becomes undermined and drops 

 Pidgeon from time to time, causing the falls to recede. The process is 

 of course extremely slow, but there is some evidence of a slight 

 change of position within half a century, while a description of 

 Niagara written in 1 678 by the Franciscan missionary Pere Hen- 

 nequin, leaves no doubt that considerable alterations have taken 

 place during the last hundred and fifty years. . . . 



It would be extremely interesting if a regular rate of recession 

 could be established, for this would enable the geologist to 

 measure the minimum lapse of time which separates us from the 

 glacial period, after whose occurrence the gorge in question was 

 commenced. But the strata already cut through are of very 

 various degrees of hardness, while in consequence of a slight 

 inclination in the bedding, the hard rock forming the present lip 

 will be at the bottom of the Falls when they have progressed 

 two miles further southward. Wind and spray will make little 

 impression on this compact limestone compared with what they 

 now effect in the soft shales, and the cataract will probably 

 remain almost stationary for ages, as has doubtless already been 

 the case more than once in the past. Hence no reliable estimate 

 can possibly be made of the lapse of time required for the digging 

 of the trench. All that can certainly be known is that enormous 

 periods have passed since the Niagara began to drain the upper 

 lakes, yet the mollusca living in its waters to-day have undergone 

 no change during all that time, as the shells found in the old river- 

 bed testify. If then, living forms have remained unmodified at 

 least as long as, and it may be much longer than, the time occu- 

 pied in cutting the gorge in question, what must be the chronology 

 of the whole geological succession to which the age of the 

 phenomena in question bears an absolutely inappreciable 

 proportion? 



The surface of the plateau about Niagara is thinly covered 

 with glacial drift, stripped of which the limestone is seen to be 

 scored all over by ice. The marks are beautifully preserved 



340 



