462 r. M. FOSHAY AND K. R. HICE — GLACIAL GROOVES. 



MiddletowD, twelve miles below Pittsburgh, is 940 to 970 feet above tide, 

 while the elevation of the same terrace as seen on the lower fifteen miles of 

 the Beaver is from 890 to 920 feet above tide. These facts, meager as they 

 are, tend to confirm the local evidence of the direction of the flow of the old 

 river toward the north, and, if any allowance whatever is to be made for the 

 postglacial elevation to the northward, seem to render any other conclusion 

 impossible. This elevation has been placed beyond doubt by the work of 

 Spencer, Gilbert and McGee, and renders it almost certain that this drainage 

 was toward the north. 



Ice Markings.— It is in the most northerly of the three Rock Point quarries 

 that we find the phenomena of special interest. This quarry lies about fifty 

 yards north of the one containing the potholes, and is similarly situated in 

 reference to the rock gorge and railroad. Almost the whole surface of the 

 rock exposed by stripping is more or less glaciated, the glaciation consisting 

 of grooves, striae, gouges, etc. 



The Home wood sandstone, forming the cliffs of the gorge, is here a massive, 

 coarse-grained rock, stained with iron, and has the characteristics which 

 make the stone of that stratum so much desired for heavy foundation work 

 in the upper Ohio valleys. It is hard and difficult to cut, and is not the 

 rock to be easily striated and grooved by an ice-sheet. On the west, the hill 

 bounding the old valley rises with unusual abruptness, and is capped with a 

 stratum of hard, massive sandstone. The quarry has been but little worked, 

 the surface which was stripped was small, and the grooves could be followed 

 but a few feet on account of the overlying gravel of the kame. The face of 

 the quarry is cut by the grooves and striae at an angle of about 60°, the 

 direction of the grooves being about southeast by south, or practically at 

 right angles to the general direction of the glacial border as heretofore de- 

 lineated.* The eroding ice must have crossed the old valley at an angle of 

 nearly 45°, descending, from the bounding hill on the west to the point at 

 which the grooves were seen, fully 250 feet in a distance of less than half a 

 mile, and yet retaining sufficient eroding power to cut great grooves, the 

 largest seen being about five feet in width and eighteen inches deep. The 

 entire surface is striated in the direction of the grooves, and, considering the 

 character of the rock, the striae are well preserved. At the quarry imme- 

 diately south of the grooves, where the potholes were seen, the surface is also 

 striated in the same direction. The strise at this point are not so well pre- 

 served, and probably were never so regular as they are at the grooves, for the 

 sandstone is here almost a conglomerate, the pebbles being very numerous 

 and reaching about half an inch in diameter. No indication of the ice hav- 

 ing affected the edges of the potholes was seen ; they are sharp as those now 

 forming in the same and similar sandstones. 



* Lewis and Wright, loc. cit., p. 194. 



