IOWA ACADEMY OF SCIENCES 
191 
The gradation downward of loess into gravel is illustrated often 
in northeastern Nebraska, near the Missouri and southwestward along 
two or three higher and perhaps older lines of drainage, marked by 
bowlder trains below the loess and by valleys with unusual sand deposits 
in them traversing the loess in a southeasterly direction. They seem 
to have been related to, the Dakota ice sheet either of the Iowan or 
very early Wisconsin stage. These are briefly discussed in Bulletin 
158, U. S. G. S., p. 61. More recent study has shown more clearly the 
bowlder trains connected with them. 
That advocates of the general aeolian origin of the loess admit this 
loess like capping, the following references show. (Udden, Iowa Geol. 
Survey, 1900 XL pp. 265-6; Calvin, Ditto, p. 446; McBride, Ditto. 483.) 
Hence we have "an almost insensible gradation from the common 
alluvial terrace to the heavy loess deposits, hence it would seem if 
some claim that there is an essential difference in the method of depo- 
sition anywhere, it should be their peculiar duty to draw the line of 
distinction and establish the criteria of distinction, 
TESTIMONY OF DIFFEEENT SIMILAR DEPOSITS. 
Another argument may be derived from the variety of deposits 
which resemble loess in fineness and distribution. One writer has 
recently found three distinct loess deposits in southwestern Iowa on 
the same hillside (Journal of Geology, XII, p. 716.) Udden admits that 
“red clay or gumbo” may be a loess and that this and typical loess 
insensibly grade into one another (Iowa Geol. Survey, XI, p. 258, and 
XIII, p. 167.) 
Now it would not be difficult to admit that quite different deposits 
should be formed by wind action, if the gathering grounds of material 
were different, but to get two or more in the same locality, would require 
either a change of climate or a marked difference in the surrounding 
surface. We can easily understand how loess of different ages should 
be much alike, for the range in size of particles carried by wind is 
small, comparatively. We can believe that there might be a gain in 
clayey character more remote from the bare surface contributing mater- 
ial, we can see how the more clayey might have a brighter and more 
permanent color, and that colors might vary with the color prevalent 
in the original source. But how by the aeolian hypothesis can be 
explained the occurrence of different strata of considerable thickness, 
clearly delimited and in close contact? And the difficulty is still more 
aggravated if they are of limited lateral extent, and more yet if there 
are three or more. 
To the aqueous hypothesis, on the contrary such facts present no 
difficulty. We have already noticed that it properly devolves upon the 
advocates of the aeolian hypothesis to show cause for claiming that 
most of the Missouri River loess is of aerial deposition when so many 
similar deposits are unquestionably of aqueous origin. 
