242 The American Geologist. October looi 
gorge has been computed by Spencer as 32,000 years ;* by 
Taylor, about 50,000 years ;t and by Hitchcock, about 19,000 
years.l Wright, from a different and independent computa- 
tion, based on the subaerial erosion and widening of the gorge 
in its most ancient northern part, conchides, as before noted, 
that its age is no more than 10,000 years. 
But there are, as this discussion has also before noted, 
ample reasons for distrusting the arguments and computations 
of Spencer and others concerning eastward outlets from the 
upper lakes, subtracting their flow from the Niagara river, 
which, as I believe, are untenable, or, at the most had only a 
very short existence. Omitting that element of the problem 
as insignificant, we have approximately 7,000 years, according 
to the diverse but concurrent computations, for the probable 
time occupied in the erosion of the gorge. 
Not satisfied with thus rejecting the hypothesis of long and 
great subtraction from the water supply of Niagara, I wish 
to direct attention to a very important cause of great in- 
crease of size of the river and falls at the beginning of the 
gorge erosion. The discharge of the river during the last 
1,000 years may be approximately represented by 1,200 or 
1,500 feet of water covering all the upper St. Lawrence drain- 
age basin above these falls. This average water supply I be- 
lieve to have been doubled or trebled during the first 1,000 
years of the river history by the added flow derived from the 
final melting of the ice-sheet, mostly 3,000 to 5,000 feet or 
more in depth, upon a very large region stretching from lakes 
Huron and Superior far north and northwest. For some part 
of this time the Niagara river probably received the outflow 
from the basin of the glacial lake Agassiz, that is, the vast 
central tract of Canada between James bay and the Rocky 
mountains. § Within its first 1,000 years, therefore, the more 
powerful Niagara may have accomplished about half of its 
gorge erosion between Lewiston and the Whirlpool. When the 
river was reduced to its present size, after its tributary ice melt- 
*Am. Geologist, vol. xiv, pp. 289-301, Nov., 1894 ; Am. Jour. Sci., third 
series, vol. xlviii, pp. 455-472, Dec, 1894; Eleventh Annual Report of the Com- 
missioners of the State Reservation at Niagara, for the year 1894, pp. 99-117, 
with maps, sections, and views from photographs. 
^Bulletin, Geol. Soc. Am., vol. ix, pp. 59-84, with two maps, Jan., 1898. 
tAm. Antiquarian, vol. xxiii, pp. 1-24, with maps and views, Jan. and 
Feb., 1901. 
§"The Glacial Lake Agassiz," Monograph xxv, U. S. Geol. Survey, 1895, 
pp. 227-244. 
