THE IOWAN GLACIATION AND THE SO-CALLED 
IOWAN LOESS DEPOSITS. 
M. M. LEIGHTON. 
One cannot work in the Iowan Drift area and in adjacent 
areas of older drift without confronting the problem of the 
loess. During the field seasons of 1914 and 1915 while asso- 
ciated with Dr. Wm. C. Alden of the U. S. Geological Survey 
in reviewing the field evidences for and against an Iowan stage 
of glaciation, the writer became interested in certain phases of 
the loess and their interpretations. Through the kindness of 
his senior colleague, the writer has the privilege of briefly dis- 
cussing these phases before the Iowa Academy of Science. A 
more complete discussion will appear in the forthcoming re- 
port of the Iowa Geological Survey in connection with the re- 
port on the investigations of the Iowan Drift, under the joint 
authorship of Doctor Alden and the writer. 
1. The Weathering of the Loess . — In the various papers 
which have appeared on the loess, little attention has been de- 
voted to the weathering of the loess. What will be said here 
will concern only that loess which is associated with the Iowan 
drift-sheet. From a careful examination of the exposures of 
the loess, it has become clear to the writer that it has been 
partly leached of its calcareous material and oxidized to some 
depth since it was deposited. The features of the average ex- 
posure where eight feet or more are shown are as follows : 
Feet 
3. Soil, black, changing below to dirty brown, no 
pebbles; usual thickness %-l% 
2. Leached loess, buff to yellow, does not react to 
dilute hydrochloric acid, no fossils or lime con- 
cretions; thickness (in some cases as much as 
12 feet) 6-8 
1. Calcareous loess, usually of lighter color than the 
noncalcareous except where grayish; the grayish 
color may not appear for several feet -below the 
top of the calcareous zone; snail fossils com- 
monly present, also lime concretions. This zone 
is usually not shown in cuts less than 8 feet 
deep. 
