PENNSYLVANIA AND DEPOSITS THEREIN. 67 



Quaker Ridge Ponding. 



■ This ponding began only when the margin of the main trunk of 

 the Kansan glacier reached a part of the ridge-crest above 1,500 

 feet, and where there was no depression beyond below that eleva- 

 tion. It was therefore far later than the Barnes Ponding, as that 

 began as soon as the old Allegheny Valley was dammed above that 

 level, and until the glacier reached an elevation on Quaker Ridge 

 also above that level, with no lower transverse troughs, the ponded 

 water to the north of the Ridge poured through the troughs, at or 

 but slightly above 1,500 feet. 



It may be asked why no account is taken of the probable lowering 

 of the Barnes trench, as its bottom to-day is at 1,300 feet. The 

 reason is that the greater part of the cutting of that trench took 

 place after the arrival of the glacial margin at Clarendon. It has 

 been said that there are two gravel terraces in the Barnes trench. 

 They consist of pieces of conglomerate, sandstone, red shale and 

 shots of limonite — all local rocks from the McKean County high- 

 lands. In addition, it has just been stated that the Indian Hollow 

 bar runs up to the surface of the shoulder of the hill at 1,488 feet. 

 It is safe to say that the Barnes Ponding was not far below 1,500 

 feet when Quaker Ridge Ponding began. 



The Conewango floodplain, at the debased end of the Ridge, is 

 filled between 1,260 and 1,280 feet for nearly 2 miles across the val- 

 'ley, and for about 5 miles along the stream. Two small islands 

 rising 40 feet above the Barnes Ponding represented the Ridge-end. 

 Randolph, Twp., N. Y., is situated at its northern end with a con- 

 tinuous barrier between the Kinzua and Conewango valleys above 

 1,700 feet; rising in spots above 1,800 feet at the northern end, and 

 to 2,100 at the southern boundary of the township, across which 

 runs the first of the trenches which relieved the ponding — that from 

 North Bone Run to Mud Creek. 



The axis of the trench is about Northwest. Its center rises to 

 1,582 feet, at a point 7^ miles from the Conewango, and almost 

 exactly on the boundary between Randolph and South Valley town- 

 ships, N. Y. Its width at 1,600 feet is 260 feet; at 1,800, 1,900 feet. 

 It is nearly 2 miles between the 1,500-foot contours, on a curve of 



