IOWA ACADEMY OP SCIENCES. 
61 
well preserved, while in the Kansan, greenstones are common 
and many of the granites are in an advanced state of decay. 
A granitic boulder more than a foot in diameter was noted 
which had been cleaved by the steam shovel without being loos- 
ened from its matrix. Sand boulders, lenses and wedges anom- 
alously distributed through the oxidized portion and often 
extending into the upper portion of the blue till are common 
features. The wedges usually maintain a more or less vertical 
position with their apices pointing downward. The filling 
material in all cases very closely resembles the sand layers 
between the Iowan and Kansan. Oftentimes the position of 
the various sand forms is such as to suggest their common 
origin with the Buchanan. In many instances stratification 
lines are common. In the trough of the hill the lower portion 
of the Kansan contains lime concretions similar to the loess- 
kindchen and ptippchen in great numbers. The lower three 
or four feet of the blue till contains wood fragments in con- 
siderable abundance in a state of almost perfect preservation. 
The physical properties of this portion of the Kansan are very 
similar to the sub-Aftonian. 
The dividing line between the Kansan and sub-Aftonian 
is more sharply marked than between the upper two drift 
sheets. In the major portion of the section the sand layer and 
the peat bed are continuous, demonstrating the extreme gentle- 
ness of the advance of the Kansan ice. It seems remarkable 
that perhaps the greatest ice sheet that ever appeared in the 
Mississppi valley could override a peat-bog with no percepti- 
ble disarrangement of materials. The pertinence of Prof. T. C. 
Chamberlin’s remark is apparent ‘ ‘ that a glacier builds its own 
causeway.” The surface of the sub-Aftonian is much more 
even than that of the Kansan; in fact it is not unlike that 
ascribed to our more modern peat-bogs. In certain places the 
upper part of the sub-Aftonian has been shifted and spheroidal 
masses of the peaty soil appear at the junction line imbedded in 
a Kansan matrix. 
Tne drift sheet below the Kansan is represented by a mass- 
ive gray -blue till with a marked greenish tone when unoxi- 
dized. The upper portion contains much humus and gives ofi 
a characteristic marsh-like odor when wet. The distinctive 
characters which serve to distinguish this boulder clay from 
the preceding are its color, the predominance of greenstone, 
and vein quartz pebbles and a less tendency to joint on 
