240 



GLACIAL FORMATIONS OF ERIE AND OHIO BASINS. 



have been cut into benches or terraces with a uniform level, and these 

 reductions from the original level of filling may easily be mistaken for it. 



The table below presents several points at which it is thought that the 

 altitude of the original surface of the gravel has been determined. The 

 table also includes points along the Ohio. 



Table showing the upper limit of gravel filling in the Lowenr Allegheny and Upper 



Ohio valleys. 



PENNSYLVANIA. 



Kennerdell 



Rockland 



Foxburg 



Monterey 



East Brady 



Red Bank 



Templeton 



Kittanning 



Ford 



Arnold •. 



Allegheny 



Beaver 



, OHIO. 



Toronto - 



Feet. 

 1,270 

 1,210 

 1,135 

 1,125 

 1,115 

 1,100 

 1,050 

 1,030 

 1,020 

 1,011 



a This represents the distance along the Allegheny; the distance along the Beaver is much less. 



The origin or mode of formation of these terraces has been a subject 

 of much discussion. At the time the hypothesis of an ice dam at Cincinnati 

 was suggested by Wright^ these terraces were cited by Lesley^ and corre- 

 sponding terraces, on the Monongahela were cited by White' in supjjort of 

 the hypothesis. But prior to that time Stevenson* had interpreted those on 

 the Monongahela and Chance^ those on the Alleghenj^ to be river terraces. 



iG. F. AVright: Proc. Am. Assoc. Adv. Sci., Vol. XXXII, 1883, p. 207; Science, Vol. II, 1883, 

 p. 664; Am. Naturalist, Vol. XVIII, 1884, pp. 563-567. 



■^J". P. Lesley: Science, Vol. II, 1883, p. 436; Second Geol. Survey Pennsylvania, Kept. Z, 1884, 

 pp. viii-xi. 



= 1. C. White: Proc. Am. Assoc. Adv. Sci., Vol. XXXII, 1883, pp. 212-213. 



*J. J. Stevenson: Second Geol. Survey Pennsylvania, Eept. K, 1876, pp. 1-22; Proc. Am. Philos. 

 Soc, Vol. XVIII, 1880, pp. 289-316. 



°H. M. Chance: Second Geol. Survey Pennsylvania, Rept. V^, 1880, pp. ix-x, 17-22. 



