52 ON THE PROBOSCIDEAN FOSSILS OF THE PLEISTOCENE DEPOSITS. 



itself, as they have become imbedded in its eroded and weathered 

 surface. As long as this till was being subjected to progressive 

 destruction, no remains of land animals could very well be pre- 

 served. They would be destroyed with it, except in special situa- 

 tions, where the general condition of erosionmay have locally come 

 to a standstill, or may have been reversed. These fossils must 

 hence be regarded as rather belonging to the stage when loess be- 

 gan to accumulate on the Kansan till. This stage is not definitely 

 fixed among the series of events of theglacial period. By some it is 

 believed to be contemporaneous with the deposition of the lowan 

 drift, but others think that much of the loess is older than this. 

 So that the only thing we can know with certainty of these fossils 

 is that they are post-Kansan and pre-loessian. They may be 

 only slightly younger than the Kansan drift, or only somewhat 

 older than some much later loess. 



There is another similar zone over the area of the Illinoi- 

 an drift. It marks in the same way the time when the loess be- 

 gan to accumulate on the lUinoian till. The conditions attendant 

 upon the beginning of loess accumulation on this till were some- 

 W'hat different from those resulting in the burial of the ferretto 

 zone on the Kansan. The lUinoisan drift surface seems to have 

 been less well drained. It is less affected by oxidation, and boggy 

 conditions were apparently more frequent when the loess began 

 to accumulate. . Only two proboscidian fossils are mentioned in 

 the list as clearly imbedded in the Illinoian drift. One was 

 found in some waterlaid material at a point one half mile south 

 of Wilton, in Muscatine county, in Iowa. This consisted of a 

 considerable part of a skeleton. The other was a tusk, occur- 

 ring just under the base of the loess, in the 'bluff near the bridge 

 across Kock river, south of Rock Island, in Illinois. The only rea- 

 sonably certain conclusion we can draw as to the age of these fos- 

 sils is that they are post-Illinoian and pre-loessial. In neither 

 case were these fossils generically identified. 



Of just as indefinite age are such fossils as have been recovered 



