IOWA ACADEMY OF SCIENCE 
225 
erect by it. It. is also evident that it could not have been laid down imme- 
diately after the retreat; of the Kansan ice sheet, because in that case it 
would have been cut away by subsequent erosion, and we would find it to- 
day only on the highlands. As a matter of fact it is as common in the low- 
est valleys' as on the crest of the divide. Therefore, if it be a purely super- 
ficial deposit, it must have been laid down after the Kansan had been 
eroded to its present contours; that is to say, in very recent times. The 
only agency adequate to this sort of post-erosional deposition is the 
wind. No aqueous agent could, in recent times, and after the erosion 
of the Kansan to its present contour, have inundated the entire country 
- — including the crest of the divide — and deposited a carpet of material 
four to forty feet thick, and then withdrawn leaving the surface other- 
wise unchanged. Such, a grotesque hypothesis needs only to be mentioned 
to be rejected. But the wind is adequate to a task of this sort. It can 
carry material up-hill. It deposits it discontinuously , . as this appears 
to be deposited. The natural first inference therefore is that the material 
is aeolian in its origin. 
The writer, at first believed this to be the case. lie has now .seen 
good reasons for correcting his conclusions. But at this point he wishes 
to insist on one thing: If the material in question is of aeolian origin, 
it is not therefore loess, any more than wind-blown sand is loess. This 
material is a joint clay, and joint clay is not loess. If it is aeolian, then 
it is an aeolian joint clay, not an aeolian loess. The term loess has 
reference to clay of a certain well-defined texture, weight, and structure, 
and this material, as has already been shown, differs from it in, every 
way. Whatever its origin, it can be productive only of confusion to 
misname it in this way. There seems to be a tendency on the part of 
some geologists to make “loess” synonymous with “aeolian material.” 
The error involved in this misuse of language 1 . has already been pointed 
out. 
THE PROBLEM' IN ADJOINING COUNTIES. 
The western part of Madison County is covered with a clay similar 
m all respects to the one herein described. It has been regarded as being 
of aeolian origin, and is described in the report on the Geology of 
Madison County as “loess.” The same is true with regard to Guthrie 
and Dallas’ counties. The author of the Dallas county report, indeed, 
was puzzled by the fact that in many places ,he found Kansan bowlders 
and gravels on top of the so-called loess. To explain this difficulty he 
was forced back upon the archaic theory of an inland post-Kansan sea, 
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