PENNSYLVANIA AND DEPOSITS THEREIN. 69 



H. L. Fairchild^ describes ponding in the Genesee Valley forced 

 by the glacial lobe up that area, over the Potter County Highlands, 

 and to the southern border of McKean County, which reached even 

 higher elevations. It poured into Allegheny Valley with more or 

 less deep and broad trenching at 1,494, at 1,600, at 1,692, and at 

 2,068 feet, and over the Potter County Highlands at 2,174, at 2,228, 

 and at 2,252 feet. 



The Big Bend Ponding poured over the McKean County High- 

 lands at many places, as can be noted from the proximity of the 

 feeders of the Allegheny and the Clarion on that plateau — the head- 

 waters of several being about 300 feet apart. The greatest de- 

 livery on the east was through the deep trench at Keating Summit 

 with bottom at 1,878 feet into the Sinnemahoning. Torrents came 

 across into the feeders of the Clarion, as will be noted below. A 

 strong flow came into the headwaters of the old Conewango : suf- 

 ficient to keep the flow from Warren to Barnes ponded between 

 Clarendon and Sheffield, and to prevent the slightest bit of glacial 

 outwash to pass over the Barnes col into the Tionesta River. The 

 Keating trench, and passes at Clermont, Glad Run and Kane, have 

 been described above. These were the most important ; but there 

 seems to have been a general movement across the plateau when the 

 margin of the main trunk of the glacier reached Big Bend, and the 

 Genesee-Sinnemahoning lobe closed the trench at Keating. Wil- 

 liams describes the results^ in the bars, high terraces, and areas of 

 sporadic gravels in the Sinnemahoning and Clarion basins, and, as 

 at Clermont, even on the plateau. Carll''' reports 43 feet of strati- 

 fied glacial outwash in the headwaters of the West Branch of 

 Clarion River. The floods seem to have carried ice-cakes, as we 

 find boulders in the stratified gravels along the Instanter Branch of 

 that stream. 



It is Leverett, however, who describes, p. 129,^ the tremendous 

 trenching of these floods from Big Bend Ponding, with their great 

 elevation : 



At the mouth of the Clarion a broad gradation plain comes in from this 

 (Clarion) valley and continues down the Allegheny to its mouth. This has 

 been trenched to a depth of about 200 feet below the level of the old rock 

 floor. The trench or inner valley is usually about one half mile in width. 



