120 TJie American Geologist. February, \m6 
In 1886, after the third survey of Niagara falls (by Prof. 
Woodward), the rate of recession was found to be much 
greater than had formerly been supposed. Prof. Gilbert then 
made a short study of the falls, the conclusions concerning 
which are summed up' as follows by that author:* "The 
problem admits of expression in an equation: 
A r I Length of gor^e. 
Age 01 gorge equals 5 & — 5 
Rate of recession of falls. 
- Effect of antecedent drainage. 
" " thinner limestone. 
" thicker shales. 
" higher fall. 
" more floating ice. 
± " " variation of detrital load. 
± " " chemical changes. 
± " " changes of river volume. 
"The catchment basin was formerly extended by includ- 
ing part of the area of the ice sheet; it may have been abridged 
by the partial diversion of Laurentian drainage to other 
courses." Pie had divided the length of the gorge by the 
maximum rate of recession, finding the product to be 7,000 
years. If the equation be carefully examined, together with 
the cited quotation, all the important changing effects in the 
physics of the river would lessen the estimated age of the 
cataract below 7,000 years, except the effect "by partial diver- 
sion of the Laurentian drainage to other courses," of which 
no evidence was suggested; nor was any lengthening of time 
shown as necessary, by the long inferior hight of the falls. 
Henceforth, Prof. Gilbert was naturally quoted as an author- 
ity that the age of the falls was only 7,000 years. This con- 
clusion did not satisfy the writer, who from the evidence of 
the beaches, especially the Iroquois, f found that the rate of 
recession must have been for long ages much less than now, 
on account of the inferior hight of the falls; and also on ac- 
count of the greatly diminished volume of water, owing to the 
overflow of the upper lakes to the northeast, until in recent 
days. But how nuich of the work of the falls had been done 
*The Place of Niagara Falls in Geological History. G. K. Gilbert. 
Proc. Am. Adv. Sci., vol. XXXV, 1886, pp. 222-223. 
■ tSee Trans. Roy. Soc. Can., 1889, p. 132; and Proc. A. A. A. S.. 
1888. p. 199. 
