256 ' IOWA ACADEMY OF SCIENCE 
contorted but which shows deposition after the disturbance of the 
gravel. This body of loess makes up the west end of the cut. 
Interpretation . — To account for such folds’ and contortions of Bu- 
chanan gravel into Kansan till in such a way as is revealed here, only 
one possible, interpretation can be given. The uniform weathering of the 
gravels at different depths in contrast to the non-uniform weathering of 
the underlying till, and the sharp contacts of the decayed gravel with 
the more or less fresh underlying till proves that the time of the dis- 
turbance was after the weathering had taken place. If the weathering 
had taken place since the disturbance there 1 should be a gradation zone 
between the weathered and unweathered portions. Such, however, does 
not exist. 
It is therefore clear that an ice-sheet, capable of distorting and mold- 
ing this hill of material, invaded this; region after the Buchanan gravel 
and some of the Kansan had been much weathered. 
In view of the above interpretation there are four important points 
embodied in this hut : first, the Kansan drift and the Buchanan gravel 
record the invasion and retreat of the Kansan ice; second, the weath- 
ering of the same represents a considerable time interval after the Kan- 
san invasion; third, the sharp contacts record the close of the interval 
and these and the folds give identity to the presence of a later ice-sheet 
and its movement; fourth, the yellow loess, at least in this exposure, was 
deposited subsequent to the advance and retreat of the later ice-sheet. 
GENERAL CONCLUSIONS. 
The last evidence seems to ‘be conclusive proof that ail ice-sheet later 
than the Kansan advanced upon the area mapped as Iowan drift. The 
significant features that were noted preceding the last evidence— namely, 
the valley-train terraces and outwash features — and the glacial topog- 
raphy of the North Liberty lobe and the bordering deposit of loess, noted 
by Calvin, add the corroborative phenomena to be expected. 
