PLEISTOCENE OF EUROPE, NORTH AFRICA, AND NORTH AMERICA 445 



Kansan time." Modern mammals: Lepus syl- 



, .. . vaticus, Mephitis mephitica. 



Light blue or graj' drift from the 



northwest, Keewatin center, covering 



large areas in Iowa. Till, sand, and pirst interglacial, AFTONIAN 



gravel boulders. 



Flats, terraces, Aftonian gravels 

 containing fluviatile and terrestrial mol- 

 luscs. Mammals: Elephas coliimhi, (?) 

 E. imperator, Mastodon americanus, 

 Sub-Aftonian Equus complicatiis, E. occidentalis, (?) 



(=pre-Kansan, Jerseyan, Albertan) Cerviis, (?) a cavicorn ruminant. Lux- 



Dark blue or black drift from the 

 northwest, Keewatin center, covering 

 large areas in Iowa. TjqDical at Afton 

 Junction. 



uriant forests of tamarack (Larix), peat 

 beds, etc. 



This table is partly compiled from the publications of Chamberlin,^ and 

 will be made more clear by a review of the latest contributions to this 

 subject by Calvin,^ who observes that within the limits of Iowa the drift- 

 ing sheets of five distinct glacial advances may be clearly differentiated. 



(1) The first is the pre-Kansan or sub-Aftonian Glaciation, which we may 

 compare with the first or Giinz Glaciation of the Swiss Alps. This was 

 followed by a long interglacial interval, knowm as the Aftonian Interglacial 

 Stage, in \vhich the ice disappeared and great floods poured along the drain- 

 age courses; especially important is the fact that the Aftonian gravels of 

 Iowa have yielded remains of a rich mammalian fauna (elephants, mastodons, 

 horses, and perhaps moose), which will be described below (p. 467); addi- 

 tional evidence to the same effect is found in the buried forests which extend 

 over practically the whole state of Iowa, in fact, the Aftonian more than 

 any other of the interglacial intervals was a time of luxuriant forest growi:h; 

 one peat deposit is three feet in thickness. (2) The second or Kansan 

 Glaciation may be compared with the Mindel and Saxonian of Europe; 

 the deposits record what appears to have been the maximum phase of the 

 Pleistocene glaciation in Iowa. This was followed by the Yarmouth Inter- 

 glacial Period, which seems to have been the longest of all the interglacial 

 intervals in Iowa ; it also w'as a true interglacial period and had its forests and 

 its terrestrial faunas; the mammals, which are sparsely known, appear to 

 have been partly of modern tyipe. (3) The third or Illiuoian Glaciation 

 affected directly only a small part of the state of Iowa. This is followed by 

 the third interglacial interval, known as the Sangamon, which is indicated by 

 buried forests, pond silts, peat beds containing great quantities of tamarack 

 (Larix) roots, etc. Though shorter than the Yarmouth, the Sangamon 



1 Chamberlin, T. C, and Salisbury, R. D., Goology. 8vo, New York, 1905-1906. 

 * Calvin, S., Present Phase of the Pleistocene Problem in Iowa. Bull. Geol. Soc. Amer., 

 Vol. XX, Mar., 1909, pp. 133-152. 



