470 GLACIAL FORMATIONS OF ERIE AND OHIO BASINS. 



valleys drift knolls appear, and in places are as numerous as in the morainic 

 tracts found in valleys farther north (described in Section IV, next chapter). 

 Several valleys are more free from knolls for a few miles immediately north 

 from the outer morainic system than they are at a greater distance. Thus 

 in the Conewango Valley the bottom and slopes are very smooth from the 

 inner border of the morainic system, nearly to Jamestown, N. Y., and there 

 di'ift knolls appear. Along Oil Creek and its tributaries the valleys are 

 quite smooth from the moraine to the sources of the creek. Along French 

 Creek there are scarcely any knolls between the inner border of the moraine, 

 8 to 9 miles below Meadville, and Saegerstown, 5 miles above Meadville. 

 On Conneaut outlet there are very few drift knolls, and the Shenango 

 Valley, in Mercer County, is comparatively free from morainic features. 

 On the uplands for 8 to 12 miles east from the Shenango, and in northern 

 Mercer County, drift knolls are very rare. 



In Ohio the greater part of Trumbull, the northwestern part of 

 Mahoning, and the eastern part of Portage counties have a nearly plane 

 drift surface, the principal exception being a morainic loop, described later, 

 which encircles the Grand River Valley. There is outside the morainic 

 loop a weak morainic belt, scarcely a mile in width, which the writer traced 

 from Windham Center, Portage County, northward to Parkman, Geauga 

 County, but could not trace farther south than Windham. It consists of a 

 series of ridges and knolls, 10 to 25 feet high, among which are basins and 

 sloughs. It perhaps represents a temporary halt of the ice margin, so 

 slight as to leave perceptible traces along only a portion of its line. 



ESKERS. 



About 2 miles west of Sheakleyville, Pa., on comparatively elevated 

 ground, near Mr. Porter's, is a sharp ridge about one-half mile long, 50 feet 

 or more in height, and about 40 rods in width, with an east- west trend. So 

 far as opened it consisted of gravel. Its form, trend, and structure indicate 

 that it is an esker, but its connection with other ridges of this type is vague, 

 and it has no fan at its eastern end. 



In the valley of Sandy Creek, east of Sheakleyville, there are two low 

 ridges side by side, each having a northwest-southeast trend and a form 

 like an esker. Neither of them exceeds 40 rods in length, 10 to 12 rods in 

 height, and 6 rods in width. It is probable that many small ridges of this 

 kind exist which have escaped the writer's notice. Their trend being at 



