62 THE NAUTILUS. 
Iowan or early Peorian. Although the pink color of the loess 
is believed to be largely original, there is some evidence sug- 
gesting that the pink loess was weathered somewhat before the 
deposition of the overlying buff loess. The interval of weather- 
ing, however, was doubtless brief. The buff loess is leached 
and oxidized at the top similar to the early Peorian loess (form- 
erly called Iowan), and this strengthens the view that the pink 
loess is Sangamon. The mammalin remains at the top of the 
till and the base of the pink loess seem most likely to be early 
Sangamon. The calcareous concretions with which they are as- 
sociated are secondary and, hence, later.’’ 
The mollusks collected embrace thirteen species of land shells, 
including two that appear to be undescribed. No lacustrine or 
fluviatile species were obtained (as would be expected), these 
mollusks being very rare or absent in true loess formations. 
Worthen’s statement of the presence of fresh-water shells may 
have referred to the genus Succinea, some species of which occur 
in the vicinity of water bodies, though the loess Succinea are of 
the upland species and not the lowland species that are abund- 
ant near water (Succinea retusa, for example). The species of 
land shells in the deposit are the same, for the most part, as 
those found in typical loess deposits in Iowa and adjacent states. 
Except where mentioned the species are normal in form. 
The division of the loess into two bodies, differing in color 
and probably attesting different periods of deposition, indicates 
that the deposition of the loess has been periodic rather than 
continuous. This is in line with the findings of Dr. Wm. C. 
Alden and Dr. Leighton in regard to the loess associated with 
the Iowan drift sheet in Iowa.+ The cause of these epochs of 
loess deposition with breaks between is still a matter of conjec- 
ture. It is the writer’s opinion that it might represent the 
presence of the Iowan ice to the north of the region. 
Dr. Leighton reports that shells were more or less common at 
all levels of the loess. The age of these molluscan remains may 
be tentatively indicated in the following table. It will be noted 
+ Alden, Wm. C., and Leighton, M. M. The Iowan Drift, Iowa Geolog- 
ical Survey, Vol. XX VI, pp. 49 to 212, 1917. 
