TOPOGRAPHY. 75 



Erie, compared with their texture in the districts farther east, accounts 

 in large part for the low altitude to which they have been i-educed. It 

 is in this basin that the Grand River glacial lobe, discussed below, was 

 developed. 



SCIOTO RIVER BASIN. 



From the western part of Lake Erie a low belt extends southward 

 through the drainage basin of Sandusky River and thence across the con- 

 tinental divide into the region drained by the Scioto River, as may be seen 

 by reference to PI. I. Its southern limits are near the city of Chillicothe, 

 where, as indicated above, the hilly country extends across to the west side 

 of the Scioto. Southward from the continental divide this lowland has the 

 form of a basin with well-defined rims on both the east and the west, but 

 from this divide northward, while the eastern rim continues prominent, the 

 western rim gradually disappears. The basin proper, therefore, lies mainly 

 within the Scioto watershed and is commonly known as the Scioto Basin. 

 It is about 75 miles in length and 40 miles or more in width. 



There is a rise of about 300 feet in passing from the shore of Lake 

 Erie southward to the continental divide near Marion. This rise is not 

 uniform, there being directly south of Sandusky an ascent of about 200 

 feet within 10 to 12 miles, while not far away on either side nearly 

 twice that distance must be covered to attain as great an altitude. From 

 this continental divide the altitude decreases gradually along the axis of the 

 Scioto Basin nearly to its southern end, but as it amounts to only about 

 200 feet in 50 to 60 miles the descent is not perceptible to the eye. From 

 the Scioto River there is a rise of about 300 feet to both the east and the 

 west within a distance of 20 to 25 miles, yet this rise is scarcely perceptible. 



The eastern rim of the basin is found at the west border of the hilly 

 country, where the resistant rock formations set in. It is made somewhat 

 regular by the drift filling, which conceals gaps between hills. The western 

 rim is made up in part of an old rock divide and in part of morainic accu- 

 mulations. Rock is struck at shallow depths on portions of either rim, 

 while in other portions it is covered to a depth of 250 feet, or even more. 

 The eastern rim is crossed by buried preglacial valleys leading through to 

 the Scioto Basin. It is not entirely certain that such valleys lead across 

 the western rim. Natural exposures and borings indicate that the rim can 

 have at most only narrow breaks, and it is possible that a practically con- 



