1894.] The Duration of Niagara Falls. 859 
THE DURATION OF NIAGARA FALLS. 
By Dr. J. W. Spencer. 
For the past century Niagara Falls has been considered a 
time measurer, but its greatest interest has risen since the 
growth of our knowledge of the Ice Age on acconnt of the 
expectation that in some way it can be made to tell something 
of the date of that period and indirectly of the advent of 
man, or his restrictions on account of the glacial conditions. 
The paper of which this is an abstract was primarily a physical 
study, setting forth the changing episodes in the history of the 
falls, and computing the age of the river, but leaving to others 
the application of the results in the question of early man. 
The method of determining the age of the falls is the appli- 
cation of the mechanics of the river to the various conditions 
during the changing episodes of its history, in a large measure 
discovered by the author during the last fifteen years. The 
investigation differs from those of other writers who have 
simply divided the length of the chasm, excavated by the re- 
treating falls, by the imagined or measured rate of the reces- 
sion of the cataract. At a glance, even the most superficial 
reader can understand that if the height of the cataract be first 
reduced to one-half, and then again doubled, or if the volume 
of the river be reduced to one-fourth, such variations are 
bound to produce as great changes in the rate of recession as 
are indicated by the mechanical laws; and that if the condi- 
tions have not always remained constant, then the present rate 
of retreat has not always obtained—sometimes slower and 
sometimes faster. It is this question that the paper considers 
for the first time. In the much written, but, until recently al- 
most unknown, history of Niagara River, we find that an ap- 
proximately correct estimate of the age of the falls was made 
half a century ago by Lyell, upon a conjecture of the rate of re- 
1 Abstract of a paper read before the Am. As. Ad. Science at Brooklyn, 
August, 1894. 
