PAPERS ON GEOLOGY 117 
typical, yellowish-gray, fossiliferous loess, presumably of the 
Iowan age, in places rests directly upon the Illinoian drift, and 
is overlain by 1 to 5 feet of brown, homogeneous silt, the tex- 
ture of which is similar to that of the lower loess. This brown 
loess-like clay, which in some places overlies the typical fossil- 
iferous loess, mantles the surface over all of this region, and is 
thought to indicate a less rapid rate of accumulation of the 
upper loess, the deposition of this bed being so slow as to permit 
the complete oxidation of the material while it was being laid 
down, while the lower oxidized Iowan loess is thought to have 
accumulated so rapidly that the material did not become so 
thoroughly oxidized before it was buried. The texture of the 
material is similar throughout and does not indicate any dif- 
ference in the power of the winds during the time both phases 
of loess were deposited. 
Evidence of the lack of conspicuous flooded conditions of 
the streams attending the melting of the Iowan ice sheet, is 
clearly seen in the lack of association with this drift sheet of 
outwash deposits, gravel trains, eskers, and other glacio-fluvial 
features, associated as compared with the abundance and extent 
of such water sorted deposits in association with the 
Wisconsin till, or with the earlier Kansan and Illinoian drift 
sheets. This absence is doubtless due to the very slow rate of 
melting of the Iowan glacier, which slow rate of melting prob- 
ably resulted from the prevalence of a somewhat unusually low 
temperature in the region during the melting of the Iowan ice 
sheet, and was not due to the existence of arid conditions dur- 
ing this time. 
The loess deposits demand a climate so nearly like that of the 
present that the hills and uplands were covered with vegeta- 
tion practically as today; that the winds were no more efficient 
in gathering or transporting materials than at present; that 
the land snails could live on the same forest covered hills which 
they now inhabit. These facts, together with the general lack 
of glacio-fluvial deposits associated with the Iowan drift are 
not consistent with arid conditions. It seems to the writer 
they can be better explained by assuming a slightly lower tem- 
perature during the melting of the Iowan ice sheet than at- 
tended the melting of the other ice sheets of the Pleistocene 
period, and continuation of this low temperature for a con- 
siderable time after the withdrawal of Iowa glacier, such as 
would retard for a time the establishment of vegetation upon 
the Iowan drift surface, and also delay the renewal of vegeta- 
tion over the mud flats of river flood plains after they were 
overflowed by the streams. 
