Age of Licking Narrows 
187 
down to the surface of the Black Hand formation, and it seems 
likely that its stream was flowing at this level when its action was 
increased by the tilting, probably near the close of the Pliocene, 
and the gorge started to develop in the bottom of the valley. As 
soon as this gorge had been cut back to where it could tap a trib- 
utary of the west-flowing drainage system, stream reversal com- 
menced in the Scioto system. This was a slow process, and how 
far it had reached before the ice invasion is not known. The 
difficulties of working out these details are many, because the 
changes were greatly complicated by glaciation which soon fol- 
lowed the adjustments started by the differential tilting. 
These discrepancies between the phenomena of the region and 
the hypothesis that the reversal of drainage was due to glaciation, 
together with the accordance of the phenomena with the theorv 
of pre-glacial capture due to differential tilting, lead us to the con- 
clusion that the Licking Narrows at Black Hand, Ohio, are of 
pre-glacial age. 
Geological Department, 
Denison University, 
December, 1908 
