218 
IOWA ACADEMY OF SCIENCE 
No Nebraskan drift was found exposed. If present at all it should 
be looked for beneath the river deposits. Unfortunately for complete 
observation the cuts are, of course, in the hills only, while fills occupy 
the valleys. 
Beds referable to the Aftonian interglacial deposits are found only 
at Avon in the deepest portion of the gravel pits. No sections of bog 
nor of peat are revealed. At the crossing of Wolf creek (Tp. 71 N., 
R. XXI W., Ne. 34 of the Sw. 14 of section 28) the creek in changing 
its channel has cut into a dark, somewhat stratified deposit, resembling 
an Aftonian deposit found in the Simpson College well; but there is 
no evidence at present at hand to determine the age of this deposit at 
Wolf creek. 
The weathered phase of the Kansan drift is frequently exposed from 
Carlisle to Chariton. South of the high hills of Des Moines strata along 
Whitebreast creek all the deep cuts into the Kansan reveal bowlders of 
stratified sand, the planes of stratification dipping in different direc- 
tions in even adjacent bowlders. The porosity of the sand bowlders 
has made it possible for surface water to reach various parts of the 
clay readily and help extend the zone of oxidation, the relative absence 
of sand bowlders in the deeper portions seeming one reason why those 
deeper portions have been less oxidized than the more sandy portion 
above. 
The Gumbo; Dallas Deposits. One of the most important relations 
which this series of exposures illustrates is the relation of the gumbo to 
the previously recognized Kansan drift. The gumbo as exposed along 
the railroad is a blue clay of varying thickness up to ten feet, without 
stratification, and with small pebbles chiefly of quartz and granite here 
and there in it, but compared with the ordinary Kansan drift almost 
pebbleless. From relations along the railroad the gumbo appears closely 
related to thie Kansan drift, in places not separable from it and in other 
places partly or wholly absent, its place being taken by stratified sand. 
In Clarke county what is apparently the same kind of a deposit is found 
definitely at lower levels in places where its position does not seem due 
to wash and creep. The only conclusion that seems applicable is that 
this gumbo was laid down not only on the upland but in places, at 
least, along drainage lines determined before the gumbo was laid down. 
As those drainage lines are on the Kansan drift, they, and the gumbo 
which is in them, must be post-Kansan in age. While the gumbo has 
not been traced across the state mile by mile, the work in the different 
counties seems to make it clear that this gumbo of south central Iowa 
corresponds to the gumbo of southwestern Iowa, which gumbo Shimek 
