THE LOESS OF SOUTHWESTERN IOWA 719 



The reddish-yellow loess reported' by Udden from Mills county is 

 probably a modification of the red loess; the ferruginous, weather- 

 stained loess reported by Calvin^ as occurring in Page county under 

 the yellow loess, and separated from it by a layer of cross-bedded 

 eolian sand, can scarcely be anything else. The white loess will 

 probably be found to have a wide distribution ; it, or a loess very much 

 like it, is to be found under the yellow loess in Carroll county.^ 

 Bain and Tilton^ have casually mentioned the occurrence of two 

 sheets of loess at different points in southern Iowa. One of these is 

 probably the white loess. The white loess is also reported from 

 Pottawattamie county by Udden, who, however, thought it to be a 

 modification of his gumbo. As the. width of the area of overlap of 

 these two sheets of loess appears to be rather limited, Udden probably 

 did not see them in the same vertical section, and hence his failure to 

 recognize them as distinct deposits would be accounted for. A very 

 interesting suggestion is contained in the fact noted above, namely, 

 that the red loess does not seem to extend far to the east of Red Oak, 

 while the white loess apparently thins out to the west of the same 

 place. The suggestion is that a deposit of loess may have fairly 

 definite boundaries, which may be imposed on it by vegetation in 

 much the same way as vegetation imposes hmits to the spread of the 

 drifting sand of a dune area. 



The red, the white, and the yellow loess are not different phases 

 of one original loess which has undergone secondary modification 

 since its deposition. A view affirming the contrary would be negatived 

 by the reflection that changes produced by weathering or interstitial 

 deposition of material by infiltration would not be hkely to simulate 



term borrowed from agricultural terminology. "Gumbo" properly means a stiff, 

 impervious, waxy, clay -silt, which the red loess certainly is not. It is an open question 

 whether the red loess was deposited as such, or acquired its red color through subse- 

 quent oxidation of its iron content. On the other hand, there exists the possibility 

 that it consists of the finer particles sorted out of the red ferretto and carried by the 

 wind to new resting-places. It would therefore be local in origin; the other loesses 

 are, however, clearly foreign. 



I Ibid., Vol. XII, p. 167. 2 Ibid., Vol. XIII, p. 445. 



3 Verbal communication from Professor B. Shimek, and later verified by personal 

 inspection. Both sheets of loess are well shown in the railroad cuts southwest of Carroll. 



4 0^. aV., Vol. VII, p. 523. 



