THE LOESS AND THE LANSING MAN. 345 



who have made the earth's surface in the loess-covered region 

 conveniently 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, lives in a few restricted and 

 widely separate areas,* invariably upon high grounds in hilly 

 country covered with abundant vegetation. Succinca 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 living on low alluvial bottom lands. 



Such forms as VaUonia gracilicosta, Strobilops virgo, Len- 

 cochcila falla\\ Bifidaria Jwhiiigeri, B. ciirvidcns, Cochlicopa 

 hibrica, Vitrea indentata, Succiiiea avara, Pyramictula alter- 

 nately and P. perspectiva, of our northern loess, and most of 

 the species 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 be underestimated, and the value of such testi- 

 mony must be placed far above merely supposed phenomena 

 for the support of which there is no direct evidence, but which 

 are necessary to sustain a theory. Fossil shells are not rare 

 in the loess. They are as widely and as generally distributed 

 in that deposit as their modern prototypes are upon the sur- 



*At Iowa City, Eldora and Dubuque, and in Allamakee, Clayton, 

 Howard, and Winneshiek counties in Iowa; Winona, Minn. ; and iso- 

 lated localities in Wisconsin, Pennsylvania, Virginia and Tennessee, 



tSee Am. Geol., vol. xxx, p. 290, etc,, 1902. 



