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Indiana University Studies 



The pre-glacial physiographic history of southern Indiana 

 is concerned mainly with the development of the old Kirks- 

 ville peneplain and the partial erosion cycles that follow it, 

 one of which was of sufficient duration to develop local pene- 

 plains below the older one. The ''American Bottoms" region 

 does not have developed in it any recognizable gradation 

 planes or local peneplains below the Kirksville plain, and in 

 so far fails of being a type unit. Stream trenching proceeded 

 below the present valley level of the main streams. This is 

 shown in the ''American Bottoms'' region. Succeeding the 

 stream trenching there was a period of valley filling. The 

 ordinary interpretation of this valley filling is that it is due 

 to regional depression. An alternative view is given in this 

 paper, in which the valley filling is ascribed to delta building of 

 the master stream, the Mississippi, extending the stream south- 

 ward into the Gulf Embayment. This delta building took 

 place during the Pleistocene, and preceded the Illinois glacial 

 invasion into the Indiana region. 



The coming of the Illinois Glacial Lobe into the southern 

 Indiana region, overriding the west fork of White River and 

 going beyond up the minor drainage basins, thus blocking 

 them either temporarily or permanently, was another impor- 

 tant factor in southern Indiana physiography. Streams all 

 along the western margin of the ice sheet were frequently 

 deranged to such an extent that they never recovered, and 

 sought new course3. Practically all streams show the effect 

 of blocking. The "American Bottoms" region illustrates 

 streams that were blocked by the glacial ice, but recovered 

 from it almost entirely, showing now only the effects of hav- 

 ing been filled some 30 to 50 feet in their lower courses, on 

 account of the valley train in the west fork of White River. 

 Beech and Plummers creeks are of this type. The lower part 

 of Cliffy Creek valley was completely filled by an outwash 

 apron, as was likewise the case in the lower part of the pre- 

 glacial "American Bottoms" valley. These valleys were laked, 

 but Cliffy Creek soon sought a new outlet to the southwest. 

 The "American Bottoms" lake never overtopped the outwash 

 barrier at the lower end of its valley. 



Following the Illinois glacial epoch. Beech and Plummers 

 creeks gradually removed most of the silt which had accu- 

 mulated in their valleys. They were able to do this because 



