54 REV. PROF. Q. F. WRIGHT, ON THE INFLUENCE OF THE 
while post-Tertiary time, which includes both the Glacial and 
post-Glacial Epochs, is probably not more than one-thirtieth of 
the Cainozoic Period, which would be 50,000 years. But even 
if this is doubled, and 100,000 years is allowed for it, the post- 
Glacial Period, which is certainly not more than one-tenth as 
long as the Glacial, would be only 10,000 years. 
We are, however, not dependent on speculative calculations 
alone to bring the close of the Glacial Epoch down to so recent 
a period that it is injected far into that of human history. 
Within the past twenty-five years, innumerable data have 
accumulated in America to prove that the ice of the Glacial 
Epoch lingered over the northern part of the United States as 
far south as the 43 degree of 1ST. latitude as late as 7,000 years 
ago. This evidence is so clear and of such a varied character 
that it cannot be resisted when once it is clearly understood. 
The evidence naturally falls under five divisions : — 
1st. The small recession of post-glacial waterfalls. 
2nd. The small enlargement of post-glacial river valleys. 
3rd. The limited extent to which post-glacial lakes, ponds, 
and kettle holes have been filled with sediment. 
4th. The small amount of the sub-aerial erosion of the 
surface of limestone rocks in post-glacial time ; and 
5th. The identity of the flora of glacial with that of the 
present time. 
1st. In America, at least, nearly all the waterfalls are in the 
glaciated region, and have been produced by the damming up 
of pre-glacial water-courses with glacial debris, so that the 
drainage is diverted into new channels where we can estimate 
the amount of erosion which has taken place since the with- 
drawal of the ice. The Falls of Niagara and those of 
St. Anthony in the Mississippi River at Minneapolis are among 
the most spectacular of the instances at our command, but they 
are by no means the only ones. The waterfalls in the United 
States which have been produced by obstruction of the pre- 
glacial drainage by the irregular deposit of glacial debris, are 
numbered by the thousand, and everywhere illustrate the 
limited amount of work accomplished by streams since the 
Glacial Epoch. But in none can calculations be so easily made 
as in the cases of Niagara and the Falls of St. Anthony. 
In pre-glacial times the drainage of the Lake Erie basin 
followed a channel leading to the head of Lake Ontario fortv 
or fifty miles west of the Niagara. This had been occupied for 
such an enormous period that the Lake Erie basin was drained 
