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Indiana University Studies 



lengthening this master stream during the Pleistocene by 

 several hmidred miles. Streams that previously emptied into 

 the trunk stream, and which had been graded in conformity 

 with a sea-level base toward the head of the Gulf Embay- 

 ment, now had to readjust themselves to a trunk stream that 

 had built or was building its bed high above its original level 

 at the place of its former entrance into the sea. It is quite 

 likely that the delta building of the master stream caused 

 the entering streams to build up their beds and valleys 100 

 feet or more in their middle and lower well-graded courses. 



This process of delta extension and attendant valley ag- 

 gradation lasted thruout the Pleistocene, and into Recent 

 times. The delta has extended itself at present so far beyond 

 the original embaj'^ment that wave erosion is probably too se- 

 vere for the process to continue. It is contended, however, 

 that the chief delta building was during the earlj^ ice advances. 

 It is thought that the Wisconsin glacial epoch contributed 

 little to actual delta extension. Notable deposits, however, 

 must have been made. The Wisconsin valley train is a rather 

 feeble one at the junction of the Ohio with the Mississippi, 

 probably less than 30 feet thick. This latest ice advance 

 nevertheless did contribute to valley filling in that it gave 

 rise to a peculiar system of lakes in the tributary streams, 

 due to the valley train and glacial flooding in the master 

 stream. Shaw^^ has described this laked condition of the 

 tributary streams and assigned it to the Wisconsin glacial 

 epoch where it undoubtedly belongs. Shaw, however, states 

 that valley filling amounts to about 150 feet, but shows that 

 the condition which gave rise to the lakes could not account 

 for more than 40 feet. He dismisses the effect of delta exten- 

 sion as inconsequential, and makes no attempt to apply it 

 beyond the Wisconsin glacial epoch. 



The following direct evidence indicates the time of valley 

 filling. In collecting data with respect to the occurrence of 

 coal seams in the region of Eel River valley in southwestern 

 Clay County, Ind., J. G. Liston, of Lewis, Ind., has obtained 

 a large number of drill hole records. A large number of 

 these show that Eel River is a valley filled 100 feet or more 

 above its bed-rock floor. A few of these records show that 



^1 E. W. Shaw, Newly Discovered Beds of Extinct Lakes in Southern and Western 

 Illinois and Adjacent States. Bulletin 20, Illinois Statr Geological Survey. 1915. 



