IOWA ACADEMY OF SCIENCE 
245 
Certain other points in Professor Todd’s paper are worthy of at- 
tention. His closing statement concerning the relative abundance 
of loess on the east and west sides of the Missouri river is aston- 
ishing in view of his experience along that stream. Surely anyone 
who has taken the trouble to compare the deposits of loess on the 
opposite sides of the river at St. Joseph, Mo., and Wathena, Kan. ; 
at Forest City, Mo., and Rulo, Neb.; at Pacific City, Iowa, and 
Plattsmouth, Neb.; at Council Bluffs, Iowa, and Omaha, Neb. 
(where the difference seems to be least of all, but is nevertheless 
striking) ; at Missouri Valley, Iowa, and Blair, Neb., and at 
Sioux City, Iowa, and opposite Nebraska points, will scarcely speak 
of a merely “slight excess” on the eastern side, when in fact the 
loess on the east side is almost uniformly very much thicker, as it 
is along the eastern side of the Mississippi river. So far as the 
writer’s observations show, the thickness of the loess on the east 
side of the Missouri river averages fully twice that on the west 
side, though it must be borne in mind that it is extremely difficult 
to give exact ratios as the loess is very variable in thickness on 
both sides of the river. But that the average thickness of the loess 
is greater on the eastern sides of the Mississippi and Missouri 
rivers is undoubtedly true. This, together with the evident close 
relationship between the distribution of both the loess and its 
fossils, to the modern distribution of plants which is determined 
largely by the same forces, and the fact that enormous amounts 
of dust are now gathered from the bars of such streams as the 
Missouri, all furnish strong proof that the greater part of the 
materials of the loess were gathered in the form of dust from river 
bars. They are not consistent with the suggestion that the mate- 
rials originated on the dry western plains, and moreover it should 
be borne in mind that by far the greater part of the loess in the 
Mississippi drainage occurs along streams which drain drift-cov- 
ered areas, and that in composition the loess is practically identical 
with the fine materials of the drift.* 
The advocates of the aeolian hypothesis therefore decline to fol- 
low Professor Todd’s suggestion to search on the dry western 
plains for the source of the loess materials. 
Professor Todd’s argument based on the formation of river ter- 
races would have greater weight if the loess was restricted to the 
terraces along the Missouri and other streams. But fossiliferous 
* Compare analyses of glacial clays, p. 250, and loess, p. 282, in the 6th An. Rep. U. S. 
Geol. Sur., 1885, Chamberlin and Salisbury. 
