SOME SUBORDINATE RIDGES OF PENNSYLVANIA 



HARRY N. EATON 

 Syracuse University 



The topography of the folded mountain district of Pennsyl- 

 vania consists of the narrow valleys and long, even-crested ridges 

 cut by occasional water gaps and wind gaps which are familiar 

 to the geologist and geographer the world over. For nearly a 

 third of a century, since the publication of the epoch-making essay 

 by Davis,' this region has been classic for the study of the pene- 

 plain. The tops of the even-crested ridges are said to represent 

 the remnants of a surface which has been variously named the 

 Cretaceous baselevel lowland/ the Schooley peneplain,^ and the 

 Kittatinny peneplain.'' With the precise dates of formation of 

 this supposed peneplain and the valley lowlands, generally called 

 the Harrisburg peneplain, ^ we are not concerned here. 



The formations sufficiently resistant to be ridge makers in 

 Center County and neighboring counties are the Oneida and Medina 

 sandstones of the earlier geologists, now known as the Oswego 

 and Tuscarora respectively, separated stratigraphically by 490 

 to 850 feet^ of the Juniata formation, consisting of soft red shales 

 and sandstones. Of the two sandstones the Tuscarora is by far 

 the more resistant to erosion, and accordingly in many instances 



^W. M. Davis, "The Rivers and Valleys of Pennsylvania," Nat. Geog. Mag., 

 I, No. 3 (1889), pp. 183-253. 



^Ibid., p. igS. 



3 W. M. Davis and J. W. Wood, Jr., "The Geographic Development of Northern 

 New Jersey," Boston Soc. Nat. Hist., Proc, XXIV (1890), 377. 



•^ Bailey Willis, "The Northern Appalachians," The Physiography of the United 

 States, Nat. Geog. Soc, Mon., I, No. 6 (1895), p. 189. 



5M. R. Campbell, "Geographic Development of Northern Pennsylvania and 

 Southern New York," Geol. Soc. Am., Bull., XIV (August 5, 1903), 283-84. 



^ E. S. Moore, Unpublished data. Also Charles Butts, "Geologic Section of 

 Blair and Huntingdon Counties, Central Pennsylvania," Am. Jour. Sci., XL VI 

 (September, 1918), 536. 



