THE IOWAN DRIFT 581 



While admitting, then, all that may be claimed for the frequent 

 references to the Aftonian soils, forests, peats, and gravels, it must 

 also be admitted that the descriptions in the early texts, which treat 

 of the texture, color, and petrological contents of the Kansan and 

 the Iowan, are based on observations made on two super-Aftonian 

 drifts. If there could remain a particle of doubt on this point after 

 reading the texts, the doubt would be dispelled by an examination 

 of the map opposite p. 727 of The Great Ice Age. The drifts of the 

 two areas represented as Kansan and Iowan respectively are both 

 super-Aftonian, and, considering the state of knowledge at the 

 time, the map is remarkably correct. The eastern edge of the 

 Iowan could scarcely be better drawn today. With the exception 

 of a few points which would be mere microscopic dots on a map of 

 this scale, the whole area mapped as Kansan is covered with super- 

 Aftonian till. There is not a single known natural outcrop of 

 sub-Aftonian in the Kansan area east of the Iowan margin. There 

 are no known outcrops of sub-Aftonian in Illinois, Missouri, or 

 northeastern Kansas where the map shows extensive areas of 

 Kansan. It is only very recently that the presence of sub-Aftonian 

 has been demonstrated in Nebraska; but even here it occurs in 

 vertical sections at the base of bluffs, in such position that it could 

 not well be represented on maps of moderate size. In Nebraska, 

 as in practically all the rest of the area mapped as Kansan, it is 

 a super-Aftonian drift that occupies the Kansan area on the map. 

 In all the earlier texts and maps it is a super-Aftonian drift to which 

 the name Kansan was most persistently and most consistently 

 applied. 



EFFECTS ON TEXTS AND MAPS OF MAKING CERTAIN PROPOSED 

 CHANGES IN THE USE OF THE TERMS KANSAN AND IOWAN 



As has been said, the imperfection of knowledge at the time the 

 Iowan and Kansan drifts were named led to confusion and incon- 

 sistencies of statements, and these are of such character and extent 

 as to make it now utterly impossible to apply the proposed names 

 in any conceivable way that will be in full accord with all the state- 

 ments of the texts. The frequent and positive references to the 

 horizon of the gravels and forest beds must be admitted and must 

 be given full weight in determining the particular drift sheets to 



