446 



THE AGE OF MAMMALS 



interval seems to have been a very long one. (4) This interval was fol- 

 lowed by the fourth or lowan Glaciation, of lesser extent, the glaciers 

 stopping a long way short of their predecessors, the Kansan and pre- 

 Kansan, the main body failing to reach the state of Iowa. This was fol- 

 lowed by the short Peorian Interglacial Stage. (5) The fifth or Wiscomin 

 Glaciation (at some points divided into two, or into early and later Wis- 



FiG. 193. — Cox gravel pit near Missouii \ allr 

 overlaid by {K) Kansan drift. 



, l(Ava. .Slanviug (.-1) Aftonian gravels 

 Photograph by Calvin. 



consin stages) sent one ice sheet into Iowa; in general, while not the 

 most extreme, it is the most conspicuous in its results, since it was this 

 last glacial advance which sent the 'great terminal moraine' across the 

 continent. 



There is no escape from the conclusion, continues the same author, that 

 the Pleistocene was a long period, compared with which the recent period, 

 or post-Glacial time, would have to be represented by a very small fraction. 

 Even the interglacial intervals, the Yarmouth or Sangamon, exceed the 

 time which has elapsed since the last, or Wisconsin Glaciation, to the present 

 day. According to this view, we may now be living in an interglacial 

 period. 



Similar views have recently been expressed by the Canadian geologist, 

 A. P. Coleman.^ This writer observes that the study of the Canachan 

 interglacial deposits supports the theory that the Ice Age is not a unit, but 

 that in the East it included several glacial periods completely separated by 

 warm periods free from glacial ice. These imply a great complexity and a 

 very long duration for the Pleistocene. The whole epoch must have re- 



1 Coleman, A. P., Interglacial Periods in Canada. Intern. Geol. Congress. Mexico, 1906. 



