The Ohio Naturalist. 
[Vol. IV, No. 7 , 
ISO 
of the valley 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 valle}' 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 recentlj" located 
it about half way 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 bj’ 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. 
Tig. I. Map showing drainage changes in the headwaters of the 
Hocking River. 
Big Rush Creek is a large tributar}’ entering the Hocking from 
the east at Sugar Grove. It rises near New Lexington, Perry 
count)’, flows westwardly into Fairfield county, the valley widen- 
ing gradually 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 count)’ 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. Xo. 13, U. S. Geol. Survey. Drainage Modifications in South- 
eastern Ohio. p. 35. 
