62 



THE NAUTILUS. 



lowan 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 lowan), 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, gome 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. 

 Aid en and Dr. Leighton in regard to the loess associated with 

 the lowan drift sheet in lowa.f 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 lowan 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 



f Alden, Wm. C., and Leighton, M. M. The lowan Drift, Iowa Geolog- 

 ical Survey, Vol. XXVI, pp. 49 to 212, 1917. 



