40 



Indiana University Studies 



The lower course of Clifty Creek, as has already been 

 explained in some detail, was also evicted from its pre-glacial 

 channel. The lake produced in its middle and upper reaches 

 extended to within a short distance of the village of Cincin- 

 nati, and the waters rose to an elevation of about 650 feet. 

 At this elevation the water evidently found an outlet across 

 a sag in the ridge to the south, and the draining stream de- 

 bouched, as it does today, nearly one and one-half miles 

 farther up Plummers Creek than in Pre-Illinoian time. 



Both Plummers and Beech creeks were also dammed by 

 the ice. These streams still discharge thru their pre-glacial 

 valleys. The presence of silt terraces in the valley of the 

 former, some 40 feet above the present valley flat, indicates 

 that it must have been effectively dammed for a time, but 

 that the barrier was not sufficiently massive to derange the 

 drainage permanently. In the lower part of Beech Creek 

 valley the terraces rise about 50 feet above the present valley 

 floor, and their presence far up the valley at a consistent 

 elevation of 600 feet shows that the valley was effectively 

 dammed to that height; but this again was not enough to 

 derange the drainage permanently. 



The close of the Illinois glacial invasion in the region of 

 the ''American Bottoms" found Plummers and Beech creeks 

 ponded some 40 to 50 feet deep, with their waters rising 

 to a level of a barrier that remained long enough to permit 

 the lakes to be filled up by the incoming debris from the 

 drainage basins above. Clifty Creek valley was so effectu- 

 ally obstructed that the water in the glacial lake found an 

 outlet approximately 100 feet above the valley of Plummers 

 Creek. The pre-glacial valley of the ''American Bottoms" 

 was also blocked to such a height that the waters confined in 

 its middle and upper portions never overtopped the barrier. 

 The surface of this lake must have had an elevation of not 

 less than 650 feet and not more than 670 feet above sea level. 



POST-GLACIAL PHYSIOGRAPHIC WORK AND 

 READJUSTMENT 



Removal of the Pleistocene Deposits. The post-glacial his- 

 tory of the "American Bottoms" region is concerned chiefly 

 with the removal of the material contributed by the glacier 

 to the pre-glacial valleys, and with the adjustment of the 



