PENNSYLVANIA AND DEPOSITS THEREIN. 61 



Conewango ponding would have escaped through the Torpedo pass, 

 as soon as the glacier at Clarendon had closed the way to Barnes, 

 and the present Allegheny would now flow up the Brokenstraw Val- 

 ley to Torpedo, thence through Grand Valley to Titusville, where it 

 would occupy the lower Oil Creek Valley, and join the Tionesta at 

 Oil City. The latter is too low as, with such an elevation, there never 

 would have been a discharge at Barnes at 1,500 feet. Washes about 

 Warren indicate that its elevation is about that of the col at Titus- 

 ville, 1,610. 



PONDINGS IN THE ALLEGHENY BaSIN, 



These can be separated into those which occurred during the ad- 

 vent of the glacial margin to Clarendon, and to the covering of the 

 Potter-McKean Plateau, and those which occurred during the stag- 

 nation and wasting of the ice there. The Barnes and Big Bend 

 pondings were in the former : that at Thompson, in the latter. 



Barnes Ponding. 



Elevation at beginning was 1,500 feet. Until the glacial margin 

 touched the spine of Quaker Ridge, there was a free passage of all 

 the ponding of the Allegheny Basin at the above elevation to the col 

 at Barnes. The main current passed from the Allegheny up the 

 Conewango to the col. The streams from the Brokenstraw Valley 

 and the short valley with headwaters at Thompson came into the re- 

 versed Conewango at Warren, and prevented the distribution of any 

 glacial outwash from the main stream west of Warren. In brief, 

 there was no flow towards Thompson. 



Just as the narrow torrents from the hopper-shaped valleys, 

 through the gaps in Bald Eagle Mountain, left long and narrow 

 ridges which rose from the level Susquehanna plain, and without a 

 general distribution of their burden over that plain ; so here, a cur- 

 rent far broader moved up the Conewango Valley from the ponded 

 Allegheny, and with increasing velocity as the glacier approached. 

 At Warren it received the clear water from the Thompson-Broken- 

 straw region and passed by Glade, Clarendon, Tiona, Sheffield, to 

 Barnes, where it escaped over the col. At Sheffield it received the 

 stronger flow from the headwaters of the preglacial Conewango, re- 



