464 p. M. FOSttAY AND H. R. IIICI^ — GLACIAL GROOVES. 



The occurrence of potholes so near at hand complicates the question not a 

 little, unless they be regarded as of different date of origin from the grooves. 

 This seems to be the proper solution of the difficulty, as they indicate a north- 

 flowing stream of no short duration, which could not have existed at the 

 time the grooves were formed if that was done by an ice-sheet. As the pot- 

 holes are immediately on the bluff of the rock gorge they must antedate the 

 time of the formation of the gorge ; for potholes are not formed on the brink 

 of a 300-foot fall. 



Beaver Falls, Pa., November 27, 1890. 



