442 GLACIAL FORMATIONS OF ERIE AND OHIO BASINS. 



access and escape of water, have jDroduced so marked an effect within a few 

 years as to render it probable that the forests or some other protective veg- 

 etation took possession soon after the ice sheet withdi-ew, and thus preserved 

 the sharp contours of the moraine. 



In Mercer and Lawrence counties, Pa., and in eastern Ohio, where the 

 morainic system is much broader than it is in Crawford and Warren coun- 

 ties, Pa., much variation is displayed. The outer portion for a width of 5 

 miles, more or less, presents a knob-and-basin topogi'aphy similar to that in 

 Warren and Crawford counties, while the inner portion has a gentle swell- 

 and-sag topography, with an occasional tract of a square mile or more where 

 morainic features are sharper. In this inner portion the higher swells are 

 20 feet or more in height, but the majority fall below 15 feet. Knolls only 

 10 to 15 feet in height often cover an area of several acres. In some local- 

 ities swells are rare, much of the surface being nearlj^ plane, but as a rule 

 they are sufficiently numerous to give the moraine a topography strikingly 

 in contrast with the plane tracts on its inner border. The outer (knob-and- 

 basin) portion in eastern Ohio and Mercer and Lawrence counties, Pa., may 

 be the equivalent of the entire morainic system in Warren and Crawford 

 counties. In that case the inner (swell-and-sag) portion is so poorly devel- 

 oped in the latter counties as to have escaped recognition. In lobes to the 

 west a full equivalent is probably found in moraines with swell-and-sag 

 topography, which lie north of the main morainic system. 



In the interlobate tract west of the Mahoning and Grrand rivers the 

 topography is bolder, with sharp conical knolls or winding ridges and hills 

 of di'ift, 30 to 50 feet or more in height, and among these are numerous 

 marshes and lakelets. The greater part of the surface is strongly morainic, 

 but, as noted above, some sipiall gravel plains occur among the knolls, 

 usually bordering the marshes and lakelets. Concerning this interlobate 

 moraine, and contrasting it with portions of the kettle moraine farther west, 

 Chamberliu remarks as follows:^ 



It is quite characteristically developed, though it has a predominant gravelly 

 constitution, and takes on the kamelike phase of accumulation. It is, however, 

 inferior in strength, roughness, and coarseness to portions of the range elsewhere. 

 This is the most pronounced development of the range in Ohio, and is the only por- 

 tion, 1 think, to which attention had been called previous to the recent geological 

 survej' of that State. 



' Third Ann. Kept. U. S. Geol. Survey, p. 339. 



