368 The American Geologist. December, 190s. 
of the great divide between the Mississippi and Missouri, is 
covered with fossiliferous loess! To periodically drain such an 
area sufficiently to leave land areas exposed for a sufficient 
length of time each year to enable a flora and a snail fauna 
to develop, would require currents so strong that much coarse 
material would be transported, and the loess would not be so 
uniformly fine in texture. 
But the absurdity of the proposition that snails could grow 
under such conditions will appeal to everyone familiar with 
their rate of growth and their habits. It may be that those who 
have made the earth's surface in the loess-covered region con- 
veniently move down and up through a vertical distance of 
300-500 feet to accommodate their theories, may find it easy to 
conceive of a change in the habits of insignificant snails, or 
may not consider their testimony of much weight. But those 
who have studied these snails in the field know that many of 
them show a remarkable persistence, in habits. Thus Helicina 
occulta, the most universally distributed loess fossil of the 
northern Mississippi drainage: MiVds 'in a' few restricted and 
widely separate areas,* invariably upon high grounds in hilly 
country covered with abundant vegetation. Succinea gros- 
venorii, also common in the loess, habitually seeks dry and 
more or less elevated surfaces, — whether in Mississippi or Ne- 
braska,— and, so far as the writer's experience goes, is never 
found on low alluvial bottom lands. 
Such forms as Vallonia gracilicosta, Strobilops virgo, Leu- 
cocheila falla.v, Bifidaria holsingeri, B. curvidens. CocJilicopa 
lubrica, Vitrea indentata, Succinea ai'ara, Pyraiuidula alternata, 
and P. perspectii'a, of our northern loess, and most of the spec- 
ies of the southern loess, t habitually frequent higher grounds, 
while all the species, without exception, which are found in the 
loess north or south, are living today upon high grounds 
which are not subject to overflow, though in some cases these 
species also extend to the lowlands. 
The fauna of the loess is not such, species for species, as is 
found today on the alluvial bottom lands along our streams, 
and it is lacking in fluviatile forms. The significance of this 
fact must not lie underestimated, and the value of such testi- 
*At Iowa City, Eldora and Dubunne. and in Allamakee. Clayton. Howard, 
and Winneshiek counties in Iowa: Winona. Minn. : and isolated localities in 
Wisconsin, Pennsylvania. Virginia and Tennessee. 
fSee Am. Geol., vol. xxx. p. 290. etc.. 1902. 
