354 S. CALVIN AFTONIAN MAMMALIAN FAUNA 



side the glaciated area would probably, at the present time, be somewhat 

 premature, but there are a few facts of some significance which may be 

 noted. The deposition of the pre-Kansan drift certainly did not take 

 place until some time after the actual beginning of the Pleistocene, and 

 yet Elephas imperator was present in the long, mild interval which fol- 

 lowed the pre-Kansan. Associated with the imperial mammoth were 

 such typical members of the Equus fauna as Equus scotti and Equus com- 

 plicatus. The camel and the M} T lodon add other faunal elements which 

 have some bearing on the question of correlation. Fragmentary and in- 

 complete as is our knowledge of the Aftonian fauna, enough is known to 

 warrant the statement that it resembles most closely the fauna of the 

 Equus zone or "Sheridan formation" as that fauna has been listed by 

 Matthew 15 and Osborne. 16 The localities from which the Aftonian fos- 

 sils have been collected are not very far from the type localities of the 

 Sheridan beds in Sheridan county, Nebraska. A statement by Scott, re- 

 markable for its insight and suggestiveness, may here be quoted. Speak- 

 ing of the Sheridan stage (Equus beds), he says : 17 



"It is, to a large extent, of seolian origin and in places contains great mi li- 

 bers of fossil bones. In South Dakota the Sheri "Ian passes under a drift sheet, 

 and probably it corresponds to one of the earlier interglacial stages." 



If, as now seems probable, the Sheridan may be correlated with the 

 Aftonian, it corresponds to the very earliest of the known interglacial 

 stages. Though it follows an interval of rather rigorous and widely dis- 

 tributed glacial conditions, the Aftonian must still be reckoned as part of 

 the Lower, or earlier, Pleistocene; for it is very old when compared with 

 the Yarmouth, the Sangamon, and the subsequent interglacial intervals. 

 To the deposits of these later stages we must look for remains of the 

 faunas of the Middle and Upper Pleistocene, if representatives of these 

 faunas are ever found in the glaciated areas. 



Postscript 



As an illustration of the fact that, owing to the rapid growth of geo- 

 logical science, it is almost impossible to get a geological paper off the 

 press before it is out of date, it may be said that since this paper was in 

 the hands of the printer a considerable amount of new material has been 



15 W. D. Matthew : List of the Pleistocene fauna from Hay Springs, Nebraska. Bulle- 

 tin of the American Museum of Natural History, vol. xvi, p. 317. 



18 Henry Fairfield Osborne : Cenozoic Mammal Horizons of Western North America. 

 Bulletin no. 361, U. S. Geological Survey, p. 85. 



17 William B. Scott : An Introduction to Geology, second edition, p. 782. New York, 

 1908. 



