386 GLACIAL FORMATIONS OF ERIE AND OHIO BASINS. 



parting between the Miami and Scioto drainage basins that it has no large 

 valleys to cross, and as the district is not so hilly as on the east border of 

 the lobe no abrupt changes in altitude occur. There is, however, a gradual 

 increase in altitude in passing from south to north, the altitude in western 

 Ross and northwestern Highland counties being about 1,100 feet and in 

 eastern Logan County 1,400 to 1,500 feet. The other members of the 

 morainic system show about the same range in altitude as the outer one, 

 the altitude of the eastern member being about 900 feet at the line of Ross 

 and Fayette counties and 1,300 feet or more in Logan County. This 

 member of the moraine may perhaps include the highest points in Logan 

 County and reach an altitude of 1,500 feet above tide, for it is possible 

 that the ice sheet extended to these high points down to the time this 

 member was forming. 



REOEF. 



In each of the several members of the western limb the outer border 

 is abrupt and quite marked, though usually but 20 to 30 feet in height; 

 but on their inner border the moraines blend into the plains so gradually 

 that there is no marked relief. The portion of this western limb in which 

 the moraines are not distinct ridges (in Logan and Champaign counties) 

 stands in places 200 feet above the valley of Mad River, which in Logan 

 County follows its outer border, but this relief is due in part to an under- 

 lying rock ridge, the thickness of the drift of the moraine being' less than 

 200 feet. There is in this poi'tion of the moraine an inner border relief 

 nearly as great as is the outer, which is also due in large part to its location 

 on the rock ridge. 



The eastern limb of the main lobe is not so distinctly ridged as the 

 western. The member that follows the water parting has a higher altitude 

 than the remainder of. the system, but this is due to a rock ridge rather 

 than to increase in thickness of drift, though the drift in this member is 

 considerably thicker than in the members or portions of the morainic 

 system east of it, and the rock ridge is interrupted by notable gaps which 

 have been completely filled with drift. 



In the shoulder east of Mansfield the thickness of the di'ift in the 

 moraine is, on the whole, markedly greater than on the tract northeast of it, 

 but so nmch variation exists that the amount can hardly be estimated. The 

 interlobate tract, thoug'h as a rule more heavily covered with drift than the 



