450 GLACIAL FORMATIONS OF ERIE AND OHIO BASINS. 



through the highest part of the kame, and the exposed section shows stratified sand 

 and gravel, with numerous bowlders up to 1 foot in diameter. 



On the western side of the Beaver, just opposite the mouth of the Conoque- 

 nessing Valle3% but more than half a mile back from the rock gorge, there are two 

 smaller kame-like deposits of graA^el which abut against the western-bounding hill of 

 the base-level plain; also at Clinton, farther southwai'd, there is another good-sized 

 kame-like deposit. All these lie on the base-level plain. 



Near the south border of these laoraiuic knolls in the Beaver Valley, 

 at the mouth of Clarks Run, a deposit of gravel sets in which is apparently 

 the outwash from the ice sheet at the Wisconsin stage of glaciation. It is 

 markedly fresher than the gravel which caps the gradation plain farther 

 south, near the mouth of the Beaver. The altitude at the head is about 875 

 feet above tide, or nearly the same as the gradation plain, but it falls to 800 

 feet in the 10 miles to the mouth of the Beaver, and the remnants of it 

 along the edge of the Beaver gorge appear at levels between 875 and 800 

 feet. This deposit at the mouth of Clarks Run has been cited by Wright 

 as a delta accumulation of the same age as the Illinoian drift in the Ohiq 

 Valley near Cincinnati, and formed in a lake supposed to have been pro- 

 duced by the obstruction of the Ohio by the ice sheet.^ But such an inter- 

 pretation can not be maintained if the deposit is of Wisconsin age (as seems 

 to be the case), for the Ohio was not oc(|upied by the ice sheet at that time. 

 The coarseness of the gravel deposits below the mouth of Clarks Run also 

 favor the view that a stream of considerable vigor was discharging through 

 the Beaver into the Ohio. 



In Little Beaver Valley, near the line of Beaver and Lawrence counties, 

 a gravel plain heads in the moraine. The latter consists of sharp knolls 

 and ridges 20 feet or more in height. It here lies back a short distance 

 from the glacial boundary, there being considerable till along the borders 

 of the valley of Little Beaver River as far south as Darlington, 2 to 3 miles 

 south of the moraine. The till in this extramorainic tract, as noted in the 

 discussion of the early Wisconsin drift, is plentiful in the lowlands and 

 around the base of the hills, but there is little, if any, on the highlands. It 

 has not a hummocky surface, like the moraine. With the exception of an 

 occasional low swell, its surface is plane. 



1 Additional evidence bearing upon the glacial history of the Upper Ohio Valley, by G. F. 

 Wright: Am. Geologist, Vol. XI, 1893, pp. 195-199. 



Continuity of the Glacial period, by G. F. Wright: Am. Jour. Sci., 3d series. Vol. XLVII, 1894, 

 pp. 162-166. 



