POT-HOLES IN ANCIENT RIVER BED 30 



Quite a number of these ancient pot-holes have been exposed as the 

 overl3dng clays and gravels have been removed in the process of quar- 

 rying, and some have also been seen on the eastern side of the Beaver. 

 All have their steep side on their southern edge, thus uniformly indicat- 

 ing a north-flowing stream. 



Differences in reported Elevations 



In the reported elevations of the old river bed there have been some 

 differences, and while all students of the subject agree that there is a 

 small fall to the northward from the mouth of the Beaver to Wampum, 

 yet a confusion of figures is apparent. This confusion seems due to the 

 fact that all have considered the rock bench along the Beaver as repre- 

 senting but one stage of the river, namely, the bed of the ancient stream 

 at the time of its reversal. This is a mistake, as an examination will 

 show that at least two stages are represented, one some 40 feet below the 

 other. These two benches are well seen at Rock point. On the eastern 

 side of the Beaver there is a bench about 100 feet above present stream 

 level.* This level is easily accessible, being the much frequented Rock 

 Point resort. The lower levels that have been reported here evidently 

 belong to this bench. On the western side of the Beaver we find, how- 

 ever, the main bench, above the level of the New Castle and Beaver 

 Valley railroad. The elevation of this road at Clinton, just south of the 

 Beaver County line, is 900 feet above tide,t and here it lies on the bed 

 rock, and at Thompsons, the next station north, the elevation is 860 feet 

 above tide,| and here the track is below the level of the old river bed. 

 The best determination of the level of the old river bed at the locality 

 of the pot-holes is 900 feet above tide. The lower levels given by White § 

 and Leverett || at Rochester, 865 feet, seem to correspond with the lower 

 level at Rock point. 



Erosion of "Inner" Valley by North-flowing Stream 



North of Wampum, in the region of the wide ''inner " gorge or valley 

 above referred to, we do not find benches corresponding to the 900-foot 

 level at Rock point, and it is suggested that the pot-holes point to the 

 reason for this absence. The presence here of the massive Homewood 

 sandstone restrained the eroding power of the north-flowing stream, 



* White : American Geologist, vol. xviii, p. 377. 

 fSec. Geol. Survey of Pennsylvania, vol. N, p. 214, 

 J Sec. Geol. Survey of Pennsylvania, vol. N, p. 214. 

 § American Geologist, vol. xviii, p. 377. 

 II U. S. Geol. Sur. Mon, xli, p. 152. 



