THE PREGLACIAL DRAINAGE OF OHIO. 31 



as they appear in this and neighboring districts. If then the 

 modifications were not produced by the glacial floods which were 

 poured over the cols into the basin, but antedate the advent of 

 these larger streams, some modifying cause must be found which 

 could have produced the changes under the action of the old 

 drainage itself. The necessary factor seems to be supplied in the 

 silt deposits which occupy the remnants of the old valleys. These 

 silts often exceed thirty-five feet in thickness. They must have 

 been deposited under exceptionaal slack water conditions. It 

 is believed that their deposition on the floors of the old valleys 

 so choked up the old drainage that it was compelled to follow 

 new lines which w^ere often over the low cols in the divides and 

 that these new lines were well established when the glacial waters 

 were poured into the basin. The limits of this paper will not 

 permit the full discussion of the problem, but it is hoped that 

 sufficient has been said to show the very great interest that is 

 involved in the study of the geographic geology of the state and 

 to stimulate further research along these lines by members of the 

 Ohio State Academv and others. 



