SAINT DAVIDS GORGE. 83 
sidered a matter of course that that gorge was made by a small stream. 
To cursory observation it may seem so, but it is believed that when this 
old gorge is closely scrutinized where its walls are exposed on the north 
side of the Whirlpool, and when the effects of glaciation in widening its 
mouth near Saint Davids are allowed their proper value and significance, 
it will appear that the preponderance of evidence favors the idea that 
this gorge was made by a preglacial or, more likely, by an interglacial 
great cataract of substantially the same volume as the present falls—in 
short, by an interglacial Niagara—and that it suddenly stopped work at 
the south side of the Whirlpool basin. 
Dr Spencer has forecast a cessation of the present falls 5,000 or 6,000 
years hence in consequence of a change of outlet of the four upper lakes 
from Buffalo to Chicago, and Mr Gilbert, proceeding on an entirely dif- 
ferent foundation of facts, has more recently forecast the same event for 
3,000 years hence.* Who can say that this prospective change may not 
be merely a repetition of what has occurred before in the last interglacial 
epoch and possibly in other earlier ones also ? 
Time Ratios 
If the whole of the Upper Great gorge was made at the measured rate 
(nearly 4% feet per year from 1842 to 1890), then it took something like 
2,700 years to make it. There is good reason to: believe, however, that 
the rate was somewhat slower most of the time, so that it would probably 
be nearer the truth to say it has taken between 5,000 and 10,000 years. 
The Upper Great gorge is three times as long as the gorge of the Whirl- 
pool rapids, so that if the latter were made at a nate one- third as fast as ” 
the former it would have taken the same time, but the volume of modern 
Niagara is about nine times that of the Erie-Niagara river during the 
Nipissing Great Lake episode. Surely, under such conditions as obtain 
at Niagara, the ratio of erosion in gorge-making would not be so low as 
1 to 3 with the volumes 1 to 9, other conditions being substantially the 
same. It seems almost certain that the time consumed in making the 
smaller gorge was very long, probably several times longer than that re- 
quired for the Upper Great gorge. The popular estimate of 7,000 to 
10,000 years for the making of the whole gorge from Lewiston up surely 
falls far short of the truth. 
For the gorge of the Whirlpool rapids no time estimate has yet been 
given that has much value even as an approximation. In one or two 
previous papers the writer has endeavored to draw aid from the example 
*J. W. Spencer: ‘‘ Duration of Niagara falls,” as above, p. 472. 
G. K. Gilbert: ‘‘ Modification of the Great lakes by earth movement,” Nat. Geog. Magazine, vol. 
viii, Sept., 1897, p. 247. : 
XIJ—Boutt, Gor, Soc. Am., Von, 9, 1897 
