76 GLACIAL FORMATIONS OF ERIE AND OHIO BASINS. 



tinuoLis preglacial divide follows it underneath the present divide. There 

 is certainlj^ a much greater general altitude of rock surface along that rim 

 than along the axis of the basin, and a somewhat higher altitude than in 

 districts to the west. 



The Scioto Basin appears to have been formed largely in the Devonian 

 shale, though the shales now cover only a small part of it, so extensive has 

 been their removal. The western rim of the basin owes its relief chiefly 

 to the resistance offered by the limestone which underlies it; but the 

 morainic ridgeb which follow it aid perceptibly in rendering it conspicuous. 

 This basin was occupied by the most prominent glacial lobe of the three 

 which were developed in Ohio, the Scioto. Its influence in causing lobation 

 is considered in the discussion of that lobe. 



MAUMEE RIVER BASIN. 



From the western end of Lake Erie a low plain about 50 miles in 

 width extends southwestward across northwestern Ohio and northern 

 Indiana, the altitude of whose rock surface is about as low as the surface 

 of the lake. The plain also extends along the south border of Lake Erie 

 into connection with the lowland tract along the Sandusky River above 

 described. Toward the south there is a gradual rise in the rock surface as 

 far as the continental divide in northwestern Ohio, and a similar rise is 

 found in passing northward into Michigan. In northei-n Indiana the basin 

 appareiitl}' extends about to the Wabash River, the altitude of the rock 

 sui'face being markedl}' higher in the district south of the river than in that 

 on the north. Its northern limits are at a line passing westward through 

 southern Michigan. 



This basin, like the Scioto, was formed largely in the Devonian shale, 

 while the higher land on its borders is underlain by more resistant strata, 

 that on the south being limestone, while that on the north is largely sand- 

 stone. At its eastern end it received the Erie or Maumee lobe, and the 

 western portion was occupied by the Saginaw lobe, which extended into it 

 from the northeast. The interlobate moraine built up between these lobes 

 rises in places over 600 feet above the level of the rock floor of the basin. 

 The di'ift filling probably averages 200 feet throughout the basin. 



