KAXSAX DRIFT OX SUB-AFTONIAN L35 



Interprt tation. — This exposure seems to show quite clearly two 

 distinct tills. The dark bluish green color of the till below the 

 old soil zone is the color of material which has undergone de- 

 oxidation from a former oxidized state. Its transition below 

 into material of yellowish to brownish color, with a greenish 

 tinge, and the presence of carbonaceous material directly above, 

 indicates that it was once oxidized but has been subsequently de- 

 oxidized, probably since the soil material has been deprived of 

 atmospheric oxygen. The leaching of the lower till to a depth of 

 about eight feet requires an interval of time, much longer than 

 post-Wisconsin -time, during which oxidation would likely have 

 taken place. Directly above the soil zone is till which has never 

 been leached or oxidized. These relations show quite clearly that 

 the deposition of the two tills was separated by an interval 

 worthy of the designation of an interglacial epoch. 



The upper till-body is unquestionably Kansan. The topog- 

 raphy of the surrounding region is not only erosional, like the 

 Kansan area, but the upper till is weathered similar to the till 

 of the Kansan area, both from the standpoint of degree and depth 

 of oxidation and from the standpoint of depth of leaching. 



Hence, if the upper till is Kansan, the lower till must be sirb- 

 Aftonian, and the soil development and leaching and oxidation of 

 the lower till must be Aftonian in age. 



The age of the stump just at the old track-level was carefully 

 considered, tipon examination of various parts of the stump 

 and its roots, it was found that the wood is mineralized with iron 

 pyrite just like fragments of wood which are scattered through- 

 out the Aftonian soil-zone. This evidence led to the conclusion 

 that the stump belongs to the Aftonian soil and was uncovered 

 in the excavation of the cut. This attention has been given to 

 the stump 3 not because it necessarily adds to the weight of evi- 

 dence for the differentiation of the two till-bodies, but it is the 

 first stump, having an interglacial position, known to have been 

 reported. 



The position of the loess above the ferretto of the Kansan 

 drift and as a mantle on the eroded surface of the Kansan drift. 

 warrants the usual interpretation that a considerable interval 

 of erosion and weathering intervened between the deposition of 

 the Kansan drift and that of the loess about the Iowan drift 

 border. 



