IOWA ACADEMY OP SCIENCE 
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yielded the interesting mammalian fauna. There are, it is true, great 
gravel deposits within the Little Sioux valley, and in places these rest 
upon the Nebraskan drift, but they are of much later age. 
It is difficult to differentiate between the Nebraskan and Kansan tills 
in the records given by well drillers but probably the major portion of 
the 200 to 300 feet or more of Pleistocene material which covers north- 
western Iowa is of Nebraskan drift. The record of a deep well on the 
upland at Cherokee is interpreted as follows: Kansan 75 feet; Nebras- 
kan 170 feet; bed-rock of Cretaceous age. 
In summary the points made by the paper are: 
1. A farther extension of the Nebraskan drift area. 
2. The Nebraskan drift of this region differs from that farther south- 
west by being of a lighter color, by being less, hard, and by being 
very uniformly low in sand and pebble content. 
3. No Aftonian gravels have been recognized in this region and it is 
thought that none exist. A clay very much like the Nebraskan 
drift, but apparently a weathered, reworked and partly sorted 
silt material, is the Aftonian of this region. 
