GLACIATION AND EROSION IN OHIO VALLEY. 121 



or even on the Scioto. The time required would seem adequate for the 

 Ohio to cut down the old divide about to the level of the Lower Ohio, with 

 which it connected, and for the Scioto to have extended its ti'enching from 

 the present mouth northward into tlie Scioto Basin far beyond the mouth of 

 Salt Creek. 



Unfortunately there is an element of uncertainty as to the age of the 

 silt which fills this trench. There is presumably a silt deposit in this valley 

 which connects at the north with the Illinoian drift and perhaps silts of still 

 earlier glacial stages. There was also in the lowan stage of glaciation a 

 widespread deposition of calcareous silt in this region, and the silts of the 

 sevei-al stages have not been properly discriminated. If it can be shown 

 that only the surface portion is of lowan age and the deeper portion is 

 Illinoian, the entire excavation would have occui-red in pre-Illinoian time 

 here, as well as in the Lower Ohio drainage system, and the two systems 

 would probably have been connected at that early date about as at present. 



ON THE UPPER OHIO. 



It remains to consider the relation which the deposits that contain 

 glacial material bear to the erosion features of the Upper Ohio. These 

 deposits are of several classes and of diflFerent ages, and are found at all 

 levels, from the rock floor under the river up to gradation plains which in 

 one place attain an altitude nearly 400 feet above it. The deposits which 

 occupy the valley bottom and rise to a height of 100 to 130 feet above the 

 stream are generall}' referable to fluvial action during and subsequent to the 

 Wisconsin stage of glaciation; but those which appear at greater heights are 

 referable to earlier Pleistocene stages. At the Wisconsin stage the valley 

 here as w.ell as farther down appears to have been opened to its full depth. 



A sheet of drift much older than the Wisconsin, and probably also 

 older than the Illinoian, has furnished material for fluvial deposits which 

 have been built up in the part of the Ohio Valley near the mouth of the 

 Beaver to a height of about 980 feet above tide, or 100 feet above the main 

 gradation plain, and 320 feet above the river. These deposits have as yet 

 been found to cover the gradation plains of the old north-flowing system 

 only as far as Toronto, Ohio, 35 miles below the mouth of the Beaver River. 

 The surface of the gravel appears, from aneroid measurements, to descend 

 in that distance 25 or 30 feet, being between 950 and 960 feet at Toronto. 



