228 
IOWA ACADEMY OF SCIENCE 
throng'll the finer with absolute uniformity. It would be more likely 
that at one point it might deposit sand only, at another boulders only, 
at another clay only, at yet another sand, clay and boulders intermingled, 
at another perhaps clay and gravel intermingled, and so forth. One 
would expect that there would be at least, a few places where there would 
happen to be little besides clay. At another place, boulders might be 
numerous in the clay. In all the vicissitudes of glacial action, this is 
the most natural expectation . 
To test this theory, and find whether it has any basis in f#et, the 
writer made some investigations of wells that have been bored in the 
Kansan and he finds that the data bear out the theory in every case. In 
the case of two wells in the town of Greenfield, the boring of which was 
watched by him, the auger passed through five and ten feet respectively 
in which no pebbles or boulders were present. These pockets of boulder- 
less clay lay at a depth of about thirty feet below r the surface. The 
material was a, stiff blue clay, unstratified, and exactly similar to the 
clay above and below except for the absence of boulders and pebbles. 
In another well bored some years ago two miles southeast of the town of 
Orient, the boring of which was watched by the writer, the entire shaft 
cut through a boulderless clay which was leached yellow above, but 
showed the stiff texture and blue color at a. lower depth; with the excep- 
tion of about three feet of boulder-bearing clay through which the 
auger passed at a depth of some twelve or fourteen feet from the sur- 
face. In these cases there was no sharp line of demarkation between the 
boulderless and the boulder-bearing clay. The one graded into the 
other. With these cases in mind the writer consulted a number of pro- 
fessional well-diggers, asking them whether as a rule the clay in Adair 
County contains boulders and pebbles or not. In every case, the an- 
swer was that, sometimes the clay contains them, sometimes not; some- 
times they will appear at one depth, sometimes at another, and it is 
impossible to predict what the condition will be in any particular 
shaft. All agree that at a depth of from fifty to seventy-five feet 
there is a forest bed, (the Aftonian) with silts and gravel present, 
and this is the only constant factor in the problem. The Kansan is 
sometimes boulder-bearing, sometimes not, and the relation of the two 
phases at any given point depends entirely upon the accident of glacial 
conditions at that point. Both sorts of material were laid down by the 
ice-sheet, and they grade into each other. 
Where the boulderless drift occurs at some depth, it consists of typical 
blue Kansan clay. Where erosion has cut into it and exposed it, it leaches 
out and becomes the so-called “loess” of Adair and adjoining counties. 
