60 
IOWA ACADEMY OF SCIENCES. 
The Iowan reaches its maxinmni 
development near the summit of the 
west lobe, where it attains a thickness 
of some ten feet. The deposit thins 
eastward. At the crest of the east 
lobe little more than a foot of Iowan 
till is present, while at the extreme 
eastern limit of the cut Iowan boulders 
are partially imbedded in the Kansan. 
The till varies from a pale yellow to a 
moderately bright yellow color, and is 
not thoroughly leached nor oxidized. 
The Iowan shows a tendency to crum- 
ble on exposure, which is in striking 
contrast to the older drift sheets. 
The line of separation between the 
Iowan and Kansan is not as well 
marked, in all cases, as could be de- 
sired but in most instances can be 
traced with some degree of confidence. 
^ In the west lobe a layer of sand 
g sharply divides the two sheets for a 
distance of 100 feet, but when followed 
in either direction becomes much dis- 
arranged by the latter and in some 
places entirely loses its identity. 
The Kansan is the predominant 
sheet in the cut and the topographic 
features of the region are faithfully 
depicted by the stiff boulder clay of 
this deposit. Its maximum exposure 
is in the east lobe, where it exhibits a 
thickness of twenty feet. The upper 
portion is oxidized to a bright yellow, 
sometimes brownish-yellow, often 
closely resembling the Iowan in color. 
The most distinctive feature in its sepa- 
ration from the latter are the char- 
acter of the included boulders and the 
greater tenacity of the Kansan till. 
The Iowan pebbles and boulders are 
prevailingly of the granite type and 
