Professor J. W. Spencer—Recession of Niagara Falls. 441 
The river at the Whirlpool was measured to a depth of 126 feet, 
but this was not quite in the middle of the current, where the depth 
is supposed to be 14 feet greater. Below the Whirlpool the river is 
shallower. From a short distance below the Falls extending to the 
Whirlpool, the bottom of the channel has a depth of about 90 feet 
below the level of Lake Ontario. 
At points a short distance within the end of the gorge and also 
beyond, a narrow, deep, inner channel, reaching to about 180 feet 
below the level of Lake Ontario, was discovered. This established 
the fact that the aggregate height of the different parts of Niagara 
Falls was more than 500 feet. 
A terrace formed upon the birth of the Falls shows that they were 
only 35 feet high. The present height is 158 feet, with a descent of 
the different parts of Niagara River reaching 326 feet. 
During the long, earlier history of Niagara, there were at first two, 
and later, three, separate cataracts. The upper two united when the 
Falls had receded about three miles; the third joined the others 
later, but it had no effect on the recession of the main Falls, as it was 
soon reduced in height by the backing of the waters of Lake Ontario. 
Until this time, when the Falls had passed the point of union by 
only 600 feet, the volume of the river was 15 per cent. of the modern 
size. Now it was increased to 100 per cent., breaking through the 
floor of the caiion to a depth of 185 feet, which the united cataracts 
had not been able to do before the increase in the volume of the Falls. 
This augmentation resulted from the accession of the drainage of 
Lakes Huron, Michigan, and Superior, which formerly drained to the 
north-east, and only now joined the Lake Erie discharge, for until 
this time Niagara received only the drainage of Lake Erie. This 
change was due to a tilting-of the earth’s crust, which culminated only 
3,000 years ago, 
The Upper Rapids are due to the river recently reopening a buried 
valley and descending over its eastern slope. This valley, however, 
did not trend northward, but southward. Accordingly, the Upper 
Rapids have had little to do with the recession of the Falls. 
Thus it appears that the rate of recession has been modified by 
changes of volume and of height. These features, and the character 
of the rock-formation, as well as the buried valleys, I now know for 
every furlong which the Falls have receded. If we apply the laws of 
erosion to these changing features the result will indicate that the 
time required for the recession of the first three miles was 35,000 
years; but for the last four miles only 3,500 years, which gives 
a total age of 39,000 years. As all the changing conditions are now ~ 
known, it appears that the probable error does not exceed 10 per cent. 
This is the only computation of the age of the Falls which has been 
made upon measurements of all the changes in the physics of Niagara 
Falls, to which no other has had access. 
Almost all of the physical changes in the history of Niagara Falls 
have been made by the writer, at different times. These, with the 
newly-found features, have now been brought together for the first 
time; and will form a monograph of the Geological Survey of Canada, 
