5 y8 SAMUEL CALVIN 



some time been calling Iowan. The third paper raises the question 

 whether, even if there is such a drift, the name it has been wearing 

 should not be applied to something else. It is possible that the 

 questions raised by these papers may never be settled to the satis- 

 faction of everyone, because men do not always see alike; but a 

 few facts bearing on the subject may be worthy of consideration. 



CAUSE OP CONFUSION IN USE OF THE TERMS KANSAN AND IOWAN 



The doubt as to the correct use of the terms Kansan and Iowan 

 is the one that deserves first and most serious attention. This 

 doubt has arisen naturally and for admittedly good reasons, but 

 it is all due to the fact that in the earlier discussions of the Pleisto- 

 cene deposits of northeastern Iowa it was assumed that there were 

 but two drift sheets east of the Wisconsin lobe which occupies the 

 north-central part of the state. The two supposed drifts were 

 named by McGee 1 the Upper and the Lower till. The view that 

 there are but two tills in this area was adopted by Chamberlin 

 in his classic contribution to the third edition of The Great Ice Age, 

 by James Geikie, 2 and the name East-Iowan was given to what 

 was assumed to be McGee's Upper till, while what was taken to 

 be the Lower till was called Kansan. There are, however, three 

 drift sheets in the region, and the attempts to describe three 

 formations in terms of two led to confusion. In some cases the 

 upper and middle sheets were described as a unit; in others the 

 lower and middle were treated as one; much more frequently the 

 lowest was ignored, and the descriptions of the "lower" and 

 " upper" tills were drawn from the other two. The presence in 

 certain localities of a forest bed or interglacial gravels, which it 

 was assumed always lay between what the authors described as 

 upper and lower tills, as East-Iowan and Kansan, complicated 

 matters still further. There are, indeed, many positive references 

 in the original texts to this forest and gravel horizon — since called 

 Aftonian — as the plane of separation between the two drift sheets 



1 Paper on "The Pleistocene History of Northeastern Iowa," by W J McGee, 

 Eleventh Annual Report of the United States Geological Survey, Part I, 1891, pp. 189-577; 

 and other papers by the same author. 



2 The Great Ice Age, 3d ed., chaps, xli and xlii, "Glacial Phenomena of North 

 America," by Professor T. C. Chamberlin, pp. 724-74, 1895. 





