720 O. W. WILLCOX 



ordinary bedding over wide areas. Conclusive evidence that each 

 is a deposit sui generis is also afforded by their stratigraphic relations ; 

 all three deposits must be regarded as unconformable the one with the 

 other as well as with the till. This is beautifully shown as regards the 

 red and the white loess in the cut just east of the depot at Red Oak, 

 where it may be seen that the red loess has been involved in erosion 

 antedating the white loess, which fills a depression previously cut 

 through the red loess into the till. Analogous evidences of a strati- 

 graphic break between the white and the yellow loess are not wanting 

 in the same neighborhood. In this connection the red loess observed 

 by Calvin in Page county may again be referred to. The layer of 

 eolian sand there separating the red loess from the yellow loess is 

 additional, if slight, evidence of the time break between the two 

 deposits. 



The inferences to be drawn from the existence of these three sheets 

 of loess and from their mutual relations are extremely interesting. 

 Considered along with the cursory references of various geologists 

 to the existence of distinct loess sheets in southern Iowa, it would 

 appear that the real complexity of the loess can no longer be doubted ; 

 "the problem of the loess" becomes, in a new sense, one of magnitude 

 and importance. Here, as elsewhere in geology, a stratigraphic 

 break is a fact of prime significance. The deeply scored surface of 

 the Kansan drift is clear evidence of a long period of time before new 

 conditions brought on the red loess; the supercession of red loess 

 deposition by an interval of erosion, followed by a period which wit- 

 nessed the deposition of a new and different loess, is sufhcient evidence 

 that the interloessial period was long enough to bring about funda- 

 mental changes in governing geological conditions. The change 

 from the white to the yellow loess has the same significance. 



It may be permissible to remark that the development of our 

 knowledge of the loess is perhaps now in about the same stage as was 

 our knowledge of glacial drift just after its glacial origin had been 

 established. At first geologists could see only one drift-sheet and did 

 not dream of more than one ice-invasion. It was only after the com- 

 plexity of the glacial deposits had been perceived that they were forced 

 to those studies which have given us our present theories of glacia- 



