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POPULAR SCIENCE MONTHLY. 



Fig. 14.— Map of the Gorge at Foster's Flats. 

 F, Location of the cross-section (Fig. 15). 



lake, but four miles farther. Again, the waters of Ontario were 

 raised and the descent of the river was reduced to the present 

 amount. Thus it is apparent that at the birth of Niagara Falls 



the cataract was much 

 smaller than now, and 

 very much resembled the 

 size of the American 

 Falls as shown in Fig. 13. 

 With the discovery of 

 the history as here set 

 forth, we had to wait sev- 

 eral years before any clew 

 was obtained as to how 

 far the falls receded dur- 

 ing each of the episodes. But at last the inquiry was partially 

 successful ; for at Foster's Flats (Fig. 14, see also Fig. 9), about 

 two miles and a half above the mouth of the gorge, the remains 

 of an old terrace occur (Fig. 15) at the height which shows that 

 the falls had receded to that point before the descent of the river 

 was greatly increased or the volume of the water enlarged to the 

 drainage of all the upper lakes. 



In this determination of the distance to which the falls had 

 probably receded before Lake Huron drained into Lake Erie, 

 Prof. Gilbert has followed the writer. Now, by applying the 

 laws of the variability of erosion to the observed modern rate of 

 recession of the falls, an ap- 

 proximate determination of 

 their antiquity became pos- 

 sible. 



Causes of Fluctua- 

 tion IN THE Volume and 

 Descent of Niagara Riv- 

 er. — In the survey of the de- 

 serted shores it was found 

 that since they were formed 

 as old water-lines they have 

 been tilted upward toward 

 the north and east at vari- 

 able rates, from a few inches in a mile at the southwest to four 

 or even seven feet per mile in the opposite direction. The phe- 

 nomenon belongs to the consideration of the history of the lakes, 

 but its effect was to tilt the lake basins so that the water ran 

 over the southern rim of Lake Huron into the Niagara drainage. 

 So, also, the tilting of the Ontario basin raised the barrier at the 

 outlet and caused the waters to rise and flood the lower lands at 

 the head of the lake, and shorten the Niagara River by four miles 



FiQ. 15. — Section of the Gorge at Foster's Flats 

 (FT, Fijr. 9). Platform {¥) of the old river floor 

 projecting into the cuiion. Its section is shown 

 in broken shiidinir, but with ravines descending 

 from both sides of it ; T, rock terrace surmounted 

 by huge blocks of Niagara limestones ; i, origi- 

 niil river terrace ; r, surface of river; L 0, sur- 

 face of Lake Ontario. Bottom of river about 

 eighty feet below ihe surface of the lake. 



