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IOWA ACADEMY OF SCIENCE Vol. XXIV, 1917 
of supply, namely the valley flats, and to the vegetation and 
topography favoring lodgment, all of which has been pointed 
out by Professor Shimek. 
The notable thickness of the loess around the border of the 
Iowan drift is too well known to demand much further refer- 
ence. The fact that it gradually diminishes in thickness and 
becomes finer as distance increases from the Iowan border, to- 
gether with the fact that it is thick even away from valleys, 
indicate that the Iowan area also was a source of supply. With- 
in the Iowan area itself the loess is generally absent or nearly 
so, but to this there are exceptions as would be expected. It 
is obvious that deposits would be made wherever there were ob- 
structions. Some such conditions gave rise to the paha, the 
wind depositing dust and sand about rock projections, glacial 
drumlins or even sand dunes. Their persistent southeasterly 
trend probably is best accounted for by assuming either that 
v the winds were prevailing northwesterlies or that the drumlins 
trended in that direction. 
If the source of the loess was the Iowan drift and the valley 
flats, and if the mass of the loess was deposited in a calcareous 
and unoxidized condition, then it must have been blown from 
the Iowan drift before the drift was weathered. This thesis 
may now be tested by noting other evidences for the age of 
the loess. 
3. The Age of the Loess . — The age of the loess can be as- 
certained by noting its relations to the Kansan drift, the Illi- 
noian drift, the Iowan drift and the Wisconsin drift. In the 
Kansan area the loess mantles the slopes as well as the uplands. 
Calcareous and fossiliferous loess in many places also overlies 
leached, oxidized, and decomposed Kansan drift. Such evi- 
dences of an unconformity tell us that the Kansan drift was 
not only weathered before the loess was deposited, but that the 
drift-plain was quite thoroughly dissected. 
The loess mantle continues into the Illinoian drift area in 
southeastern Iowa, where it shows the same amount of weather- 
ing as the loess about the Iowan border. Here it also occurs 
on the eroded surface of the Illinoian and in many places its 
calcareous zone rests on the weathered and decomposed Illi- 
noian till, there being in many places an intervening develop- 
ment of the gumbo as in the Kansan area except that it is thin- 
