188 
IOWA ACADEMY OF SCIENCES 
Again, many of these channels have sand and gravel deposits, under- 
neath the loam, lining former channels cut in the underlying till, imi- 
tating similar deposits under the loess in such locations. The surface of 
the till, was not as rough before the deposition of the loam as the Kan- 
san till was before the deposition of the loess, for the latter had been 
subject to longer and more vigorous erosion. Yet, let us remember, in 
the latter case the surface of the till is much rougher now than when 
the loess w'as laid down. There can be no doubt in the light of many 
observations, that the roughness of both the till and the loess has been 
greatly intensified by ravine cutting, as I explained in my paper on 
“Degradation of Loess”, 
This loam or silt so strongly resembling loess, is of a cream color, 
not So yellow^ or rusty looking as the loess, it is of about the same fine- 
ness, is composed mostly of well rounded quartz grains, and shows no 
sand or coarse particles except toward the base, exhibits the same ver- 
tical cleavage so often mentioned of the loess, and is usually similarly 
unstratified. In some localitiees there is quite regular alternation of thin 
loamy and clayey layers composing several feet of its depth, but often 
15 or 20 feet thickness of the loam may appear without distinct stratifi- 
cation. Pebbles are as rare on the plain of Lake Dakota as in the loess 
region of western Iowa. Only a very few knolls of bowldery drift stick 
up like islands above the loamy plain. 
.No fossil shells appear in the loam and fossils of any kind are very 
rare. Prints of leaves have been reported in its lower layers, but the 
report is not very trustworthy. 
Calcareous concretions with 'cracked interior like “Loess kindchen”, 
are not infrequently found, and also ferruginous pencil-like ones like 
those of the loess, but all these characteristics may be considered nat- 
ural results of the physical nature of loam. 
The deposit shows more frequently efflorescent salts on the surface of 
its exposures, especially tow^ard its base, but this is easily explained by 
its youth and consequent less complete leaching. 
We may therefore sum up the resemblances between the lacustrine 
loam of Lake Dakota and the loess of the Missouri valley, as follows: 
Its fineness and composition, its destitution of aqueous fossils and 
others as well, its general absence of stratification, its prevalent vertical 
cleavage, and the prevalence of cracked calcareous and of pencil-like 
ferruginous concretions. 
Its deposition like a blanket over high and low surfaces of the till, 
often with a washed surface upon the latter and with sand and gravel 
deposits along the larger channels cut in its surface; the absence also of 
any distinct barrier to hold back the depositing waters. 
It differs from the loess most in its color, larger proportion of solu- 
ble salts and in the more even surface of the underlying till, also in the 
more extended level form of its upper surface with its nearly horizontal 
position. These differences are in degree, however, rather than in kind, 
and can perhaps all be accounted for by differences in age, thickness and 
height above base-level. Besides, the loess having a much larger extent 
