1886. J vOD [Branner. 



It is scarcely credible that such pot-holes could have been formed by a 

 stream smaller thau the Lackawanna at Archbald, and this falling from 

 a considerable height. I say "falling from a height" because, while I 

 know that pot-holes may be, and are, formed in eddies by currents capa- 

 ble of whirling the wearing material inside of them, I do not imagine that 

 any one will claim that even the Lackawanna could whirl the stones in the 

 bottom of even the smaller of these pot-holes, at a depth of thirty-four feet 

 without striking the water in it from a considerable elevation. But even 

 admittiug that such a stream might have done this, we should still need to 

 account for such a stream at this place and elevation. 



At the Archbald iron bridge the Lackawanna contains the water drained 

 from a hydrographic basin having an area of one hundred and four (104) 

 square miles, and, when at an average height, this stream has, at this 

 point, a volume of 83.441 cubic feet per second. To produce such a stream 

 as this upon an area of less than two square miles, to say nothing of a quar- 

 ter of a square mile, would require a precipitation surpassing anything of 

 which we have any knowledge. Finally while the difference of elevation 

 between the upper and lower pot-holes is about sixty-five feet in a distance 

 of 1100 feet, the head of this hollow is much flatter, there being but thirty- 

 five feet fall between the head of the hollow and the upper hole — a distance 

 of about 1800' — which is clearly not enough to produce a current suffi- 

 ciently powerful to move the stones in the bottom of a pot-hole fifty feet 

 deep. 



In support of the explanation offered by Professor Lesley, I would call 

 attention to an important, and somewhat remarkable topographical feat- 

 ure in this part of the valley — a feature even more striking when looked 

 at upon the ground, than when seen upon the map. This is a hill that 

 projects, from the vicinity of the pot-hole, directly across the whole val 

 ley, in the direction of Archbald, and is only interrupted at this place by 

 a narrow gorge, through which the Lackawanna flows. 



Where the "back road," leading from Olyphant to Jermyn, crosses 

 this hill, it is 310' above the level of the river at Archbald, while 1500' 

 north-east of the lower pot-hole, it (the hill-top), is 380' above the river, 

 and 125' above the mouth of the lower bole, which is just below the crest of 

 the hill. 



The ice moving down the Lackawanna valley, and over the top of this 

 hill, must have been broken by it into crevasses into which the streams 

 that formed these pot-holes must have plunged. As the ice moved for- 

 ward, the crevasse would occur at, or about, the same point every time, 

 and so keep the water fall stationary, or nearly so. The shallow prolonga- 

 tion of the upper part of the lower hole was probably caused by the occa- 

 sional withdrawing of the stream, as it cut the ice more rapidly than it 

 was pushed forward. 



The surfaces of the rocks on the top of the hill above the upper pot-hole 

 have been worn smooth by the ice, but being friable sandstones they have 

 failed to preserve any stria?, and although most careful search was made, 



