IOWA ACADEMY OF SCIENCES. 
215 
before many of them were formed or much of the surface worn 
away. 
It might be taken for granted that the ice movement was 
from northwest to southeast as is universally conceded; but, as 
already stated, there is but little doubt that the Illinois ice sheet 
once held possession, and it is barely possible that those stri^ 
which are more nearly east and west might be its product. 
However improbable it is, while the possibility remains, the 
question is open for argument. The accompanying phenomena 
here all indicate- movement to the southeast. The depressions 
in the rock floor, caused by fossils or concretions, are more 
abrupt on the northwest side than on the southeast, and when a 
groove cuts through one of them it perceptibly widens on the 
southeast. But more conclusive evidence than this is where one 
groove intersects another. The angle to the northwest is sharp, 
clear-cut and distinct, while that to the southeast is blunted and 
rounded ofl, exactly the effect that would be expected with 
movement from the northwest. Fragments entering the inter- 
section would be somewhat freed and would strike against the 
projecting angle, thus breaking it away. It seems conclusive 
that all movement indicated by these striae, including that which 
is most -nearly east and west, was from the northwest toward 
the southeast. 
The trend of the bluff at this place is from north to south 
about 5° west. It. will be seen that the latest scratches are 
nearly at right angles to the escarpment, while the earlier ones 
cut it at a comparatively sharp angle. The inference might be 
that the earlier ice flow was entirely independent of, while the 
later one was influenced by, the local topography. The Missis- 
sippi exerted little or no influence on the earlier flow, but near 
the close of the ice age it maintained a wide, open channel 
directly into which the ice stream pushed. If this were true, 
then we ought to find the valley full of erratics and terminal 
debris. There is great probability that the boulders lie thickly 
strewn beneath the surface of the old flood plain; but they lie 
deeply, for the valley has been silted up many feet. There is 
one place, however, where, in time of extreme low water, these 
erratics may be seen in great numbers in the present channel of 
the river; also, along the line of the bluff itself there is abun- 
dant evidence. 
The other locality described in the article before referred to, 
is near West Burlington. This exposure is illustrated in figure 
