15° 



The Ohio Naturalist. 



[Vol. IV, No. 7, 



of the valle}^ about loo feet lower at Carroll than at Sugar Grove ; 

 that is, the rock floor slopes to the north in a direction opposite 

 to that in which the present stream flows. This fact coupled 

 with the shape of the valley makes it certain that prior to the 

 Glacial epoch an old divide was located somewhere south of 

 Sugar Grove. The exact site of this col has been variously 

 placed by different writers ; Prof. Tight has very recentl}- located 

 it about half waj^ between Logan and Nelsonville/ Before the 

 ice invasion a stream headed on the northern side of this divide, 

 flowed northward through the valle}- now occupied by the Hock- 

 ing, and northwest of Carroll connected with the preglacial outlet 

 of the upper Muskingum which crossed the northern part of 

 Fairfield county. After the ice blocked this outlet, the water 

 forced over the old divide at the head of the stream and in time 

 it was cut to the present level. 



BLOOI 



CLEAR CREEK 



MADISON 



/"i^. I. Map showing drainage changes in the headwaters of the 



Hocking River. 



Big Rush Creek is a large tributary entering the Hocking from 

 the east at Sugar Grove. It rises near New Lexington, Perry 

 county, flows westwardly into Fairfield count)-, the valley widen- 

 ing graduall}' until at Bremen it is three-quarters of a mile wide. 

 At Bremen it turns abruptly to the south and narrows until a 

 point in Hocking county one mile below the county line is reached. 

 Here it is narrowest, being only 200 yards in width between the 

 rock walls on either side, and the drift is only 20 feet deep. It 



4. Professional Paper. No. 13, U. S. Geol. Survey. Drainage Modifications in South- 

 eastern Ohio. p. 35. 



