164 
IOWA ACADEMY OP SCIENCE 
DISCUSSION. 
In the above description the material down to the weathered surface 
of the Kansan is what is commonly found throughout the uplands in the 
central part of the county. Parts of it correspond to what has been de- 
scribed in other places where the Kansan is the surface drift. 
From the top of this drift, at thirty-Uvo feet, down to the bottom of 
the drift at eighty-six feet the characteristics of the deposit are so like 
those of the Kansan drift, and the gradations so perfect from a weath- 
ered portion to an unw^eathered portion below, that there seems no pos- 
sibility whatever that it includes more than one drift sheet. It is there- 
fore all classed as Kansan. 
The deposit that underlies the Kansan is peculiar. The color of the 
''deposit and the xwesence of a few pebbles within the twenty-five feet, 
though the pebbles are only about half an inch in diameter, suggest sub- 
Aftonian drift; but the appearance of stratification, marked especially 
by the distinct layers of moss with accomxDanying black dirt, at least 
four of which were conspicuous, are liot characteristics of drift at all, but 
of a non-glacial deposit into which it seems possible such small pebbles 
may have been washed, though I noted no stratum of gravel associated 
with them within the deposit. Such a deposit, between a Kansan above a 
sheet of gravel below that contains glaciated pebbles, is classed as a part 
of the Aftonian interglacial deposit. The deposit appears to be a unitj 
though varying slightly close to the gravel at its base. 
The stratum of gravel with glaciated pebbles at the bottom of the well 
must have come from a glacial deposit anti dating the Aftonian. It was 
therefore derived from the sub-Aftonian (Nebraskan) drift, for no 
other drift sheet is known from which it may have come. The condi- 
tions suggest that the well reaches the bottom of- a ravine into which 
gravel from sub-Aftonian drift was washed. 
The sub-Aftonian drift is wanting at this particular place, unless a 
trace of it is left immediately beneath the streak of bright red clay. It is 
not- wanting in various parts of the county. The Kansan may be seen in 
its usual aspects in the higher ground, Avhile along the deeply cut 
trenches in ravines may be seen the dense, bluish black sub-Aftonian, 
largely free from boAvlders and pebbles. The soil Avashed from the hill- 
sides generally covers the dividing surface betAveen the two drifts and 
whatever of Kansan may remain. 
