356 The American Geologist. December, 1903. 
port this theory of the sub-glacial origin of the loess. Yet the 
living fauna of the loess-covered regions shows essentially the 
same depauperation. The comparisons which Call makes in 
the paper on the Des Moines loess are based in part, at least, 
upon measurements of eastern modern shells.* 
Had the author taken recent shells from Iowa, especially 
from the prairie sections, he would have been left practically 
without support for his conclusions. f 
The causes which produced a "depauperation" of some of 
the shells are in operation today in Iowa and adjacent territory, 
for practically all of the fossil cases may be duplicated in the 
modern fauna. 
Another source of error of a more excusable nature in the 
reports on fossils is to be found in misconception of species 
and incorrect identification. For example, what was generally 
reported on Vallonia pulchella from the loess is V a! Ionia grac- 
ilicosta, a northwesterly upland species ; under fossil Succinea 
obliqua were included two, possibly three species; Carycliiitm 
exiguum (reported as semi-aquatic by Call, in paper on Des 
Moines loess, 1. c. p. 16!) has not been found in the loess, the 
fossil species being C. exile, a decidedly upland species ; the 
form commonly reported by earlier writers as Pupa blandi is 
Bifidaria pentodon (though P. blandi occurs in the loess), and 
possibly a Vertigo; and other instances might be cited showing 
that species were not clearly recognized by conchologists, and 
in consequence comparisons of fossil shells were sometimes 
made with recent shells of different species. Manifestly con- 
clusions drawn from such comparisons are worthless. 
Both Drs. Chamberlin and Salisbury, and professor McGee 
relied upon such information and were misled by it. The 
aquatic shells of the loess are relatively very few. and all of 
that type which .inhabit small ponds. There is not a single 
well authenticated species of fluviatile mollusks known from 
clearly undisturbed loess in this country ! And yet reference 
is constantly made to the few paltry pond snails, coupled with 
vague references to "semi-aquatic" forms, while the vastly 
*The present writer, then a college student, made the drawings for the 
plate which illustrates that paper. 
tFor discussion of depauperation of shells by the present writer see : 
I'roc. hi. Arnil i,f Boi.. vol. iii. p. 85. 1896: vol. v, pp. 43-4, 1897: vol. vl, 
p. 101, 1899; Jour. Oeol. vol. vii, pp. 126, 127, 1899. 
