The Loess and the Lansing Man. — Shimek. 367 
in enormous lakes, where are their shore-lines, and where were 
the land areas which produced the terrestrial mollusks? 
d. The loess is more or less fossiliferous, especially where 
it is thickest, and where therefore the floods should have had 
greatest influence. The shells are, with slight exceptions, those 
of land snails which are not found, at least in large part, upon 
alluvial low lands adjacent to streams. Great floods covering 
such areas would render them wholly unfit for such plant life 
as these snails require. Presumably these floods would come 
in late spring and summer. How much advancement of plant 
and snail growth could be expected in the fall, winter and 
early spring? 
In his recent article* Upham makes the remarkable state- 
ment that in "the summers of each year the floods pouring 
along the valleys from the ice melting and rains added little 
to the surface of the whole flood plain ; but in autumn, winter, 
and spring, the diminished rivers flowed in comparatively nar 
row channels, probably permitting the main part of the flood 
plain to become more or less covered by grass and other vege- 
tation, and to be inhabited by air-breathing mollusks. ">" 
It is fair to presume that under the climatic conditions here 
assumed the winters were, still long, and that much ice was 
formed each season. If the streams were flooded four months 
each year, as suggested, and much of the remainder of the yeai 
was winter, when did the grass and snails grow? And, fur- 
thermore, where do modern representatives of the loess species 
of molluscs live under such conditions? 
If it is argued that the mass of loess was gradually ac- 
cumulated by a succession of floods, which periodically receded 
sufficiently to expose land-surfaces, then it is necessary to con- 
sider movements of enormous volumes of water in compara- 
tively short time, for the loess-covered regions are not in re- 
stricted depressions, and enormous floods would be required 
to cover them. In Iowa, for example, these floods would have 
covered the greater part of the state. The loess-topped hills at 
Iowa Citv are lower than the loess border near the Mississippi 
river, and the hill south of Carroll, about 275 miles west of 
Iowa City, and more than 600 feet higher, t and forming a part 
•Am. Ghol , 1. c. p. 29. 
tSubstantially the same statement had been previously made by him in 
Bull. (Ur>l. Soc.'of Am.. \nl. 5, p. 94. 
JSee R. R. profiles, Iowa R. R. Commission. 1881. 
