A NOTABLE TYPE PLEISTOCENE SECTION 



this monograph was written when the theory of the origin of the loess was 

 swinging from the aqueous hypothesis to the eolian hypothesis, and the dis- 

 cussion carries the spirit of compromise rather than the present general 

 view that the loess is dominantly eolian in origin. 



The peat of the railway cut occupies the same horizon as the old soil in 

 the Farm Creek exposure. The peat here, as Leverett points out, records 

 poor drainage conditions after the weathering of the underlying till. It may 

 well have been a local marsh, such as might result if there were relatively 

 slight irregularities in the deposition of the loess on a previous flat surface. 

 The Farm Creek exposure emphasizes the local transition that existed within 

 short distances from subsurface drainage of an oxidizing character to nearly 

 stagnant drainage of either unoxidizing or deoxidizing character. The 

 brown to grayish-yellow color of the old loesslike silt in the east part of the 

 cut is believed to represent the former condition, and the bluish-gray loess- 

 like silt with greenish cast in the west part represents the latter. The differ- 

 ence in color of this loesslike silt and the normal loess is, therefore, not sig- 

 nificant of a difference in mode of origin. 



The overlying soil was formed subsequent to the deposition of the 

 underlving loesslike silt, and before the deposition of the overlying loess. 

 Whether its development represents the full period of time involved in the 

 weathering of the underlying loesslike silt cannot be denied or affirmed. It 

 represents at least the latter part of this period, and plausibly coincides with 

 the Sangamon soils known elsewhere which are reported to contain boreal 

 vegetable remains. Such vegetation probably lived during the transition 

 from the Sangamon interglacial epoch to the Iowan glacial epoch, or even 

 during the Iowan glacial epoch. There is, indeed, reason for thinking that 

 the vegetable content of this soil and peat horizon represents the tundra 

 conditions marginal to the Iowan ice sheet. The loesslike silt is referred 

 to the latter part of the Sangamon, and the silt of Leverett's railroad sec- 

 tion is correlated with it. 



3. Horizon 5 is typical fossiliferons loess. A collection of shells was 

 made and these have been identified by Curator F. C. Baker, of the Museum 

 of Natural History of the University of Illinois, as Hclicina occulta (Say), 

 Succinca ovales (Say), and Orcohclix io7ccnsis. The shells of the latter 

 are crushed but identifiable. All three are common to the Peorian loess and 

 the first two have been found in Recent loess. Orcohclix iotvaisis, accord- 

 ing to Curator Baker, is not known in Recent loess. It is to be noted that 

 the deposit is calcareous to the top, but the oxidized state, in contrast to the 

 unoxidized basal portion of the Wisconsin drift, is in harmony with the 

 evidence at other places that an interval of weathering occurred between 

 the deposition of the loess and the overlying Shelbyville till. The Shelby- 



