DELAWARE COUNTY. 303 



the townships of Thompson, Radnor, and the northern part of Pcioto, 

 has the features of the flat tract in north-western Ohio known as the 

 Black Swamp. The banks of the Scioto are low (ten or fifteen feet), and 

 consist of Drift, the rock rarely being known in its bed. The Drift ap- 

 pears fresher and the surface is smoother than in the rest of the county. 

 A short distance above Millville the banks begin to be rocky, the exca- 

 vation beginning in the Waterlime, over which it has been running 

 since it left the western part of Hardin county, but without making the 

 slightest excavation, rarely revealing it in its bed by rapids. Within a 

 mile from Millville the arriount of erosion in the underlying rock in- 

 creases to a remarkable extent, and at Sulphur Spring Station, about two 

 miles below Millville, the erosion in the rock amounts to sixty or seventy 

 feet. From there southward' the rest of the Scioto valley is between 

 high, rocky banks. This exemption from erosion in the upper waters of 

 the Scioto can not be due to the harder nature of the rock there, because 

 the Waterlime is much more rapidly worn out under such agencies than 

 the Lower- Corniferous, on which it enters at Sulphur Spring Station. 

 The composition of the Drift about the headwaters of the Scioto is the 

 same as about the lower portions of its course. It is in both cases a 

 hard-pan deposit, made up of a mixture of gravel stones, bowlders, and 

 clay, rarely showing stratification or assortment — such a deposit as is, 

 without much difference of opinion, attributed to the direct agency of 

 glacier ice. The conclusion is inevitable that the lower portion of the 

 Scioto has been at work digging its channel in the rock much longer 

 than the upper portion. The slope is in both cases toward the south, at 

 least that portion of it in Delaware county; and that agency, whatever 

 it was, which served to make this change in the valley of the Scioto 

 from no excavation to deep rock erosion, 'could not have been quiet, 

 standing waters over one portion of the valley and not over the other, 

 since such waters would have retired last from the lower part of the val- 

 ley, and we should there expect less instead of more erosion. The only 

 possible way to explain this phenomenon, in the light of plausible theo- 

 ries, is to refer it to the operation of the last glacial epoch, or to the op- 

 eration of a glacial epoch which projected the ice field only so far south 

 as to cover the upper part of the Scioto valley, leaving the lower portion 

 of the valley, which probably pre-existed, to serve as a drainage channel 

 from the ice itself. Subsequently, when the ice withdrew, the upper 

 tributaries were located in such places as the contour of the surface 

 allowed or demanded. 



There are other evidences that the townships of Radnor, Thompson, and 

 the northern part of Scioto were for a time under glacial ice, while the 



