282 CAMPBELL — NORTH PEXNSYLVAXIA AND SOUTH NEW YORK 



be represented by the synclinal ridges, which in this region rise to alti- 

 tudes ranging from 2,200 to 2,500 feet, and that the Chemung hilltops, 

 which vary from 1,600 to 2,200 feet, may represent a peneplain of early 

 Tertiary age. 



Similar conclusions were arrived at independently by Mr L. C. Glenn 

 in the study of the Olean and Salamanca quadrangles of southern New 

 York. Although in this region the hilltops vary more in altitude than 

 in Tioga count}^ Pennsylvania, a close study reveals the fact that those 

 which lie at an altitude of about 2,100 feet in the northern part of the 

 quadrangles have very flat summits, while those which rise to higher 

 elevations are irregular and have very little flat or gently rolling land 

 upon their crests. Mr Glenn is disposed to regard the 2,100-foot con- 

 tour as marking approximately the position of a Tertiary peneplain 

 surface, while the flat tops along the state line, made by the massive 

 Olean conglomerate at an altitude of about 2,400 feet, presumably repre- 

 sent the peneplain of Jura-Cretaceous age. 



Physiographic Features of eastern Pennsylvania 



Inasmuch as the present interpretation of the physiographic history 

 of the plateau region is different from that heretofore maintained, it 

 seems advisable to review briefly the topographic features of the eastern 

 part of Pennsylvania to see whether previously they have not been 

 misinterpreted and whether a new interpretation may not be made that 

 will be in agreement with the writer's conclusions regarding the succes- 

 sion of events in the plateau region. 



The only publications dealing with the physiography of this district 

 are the papers by Davis on '' The rivers and valleys of Pennsylvania " * 

 and Davis and Wood on " The geographic development of northern 

 New Jersey." t In these "papers Davis recognizes the remnants of two 

 peneplains — one represented by the even crest-lines of the valley ridges 

 and presumably of Jura-Crustaceous age and the other of late Tertiary 

 date and developed only on the soft rocks of the Kittatinny valley and 

 on the wide outcrop of Newark rocks which forms a belt of lowland 

 across the two states. 



With these two propositions the writer is in entire accord ; therefore 

 it is unnecessary to review the evidence on which they are based ; but 

 the point of difference is the recognition by the writer of a peneplain 

 lying between those described by Davis, which is less extensive than 

 the Schooley (Jura-Cretaceous) and much better developed than the 



* National Geographic Magazine, vol. i, pp. 184-253. 



t Boston Society of Natural History, Proceedings, vol. 24, pp. 365-423. 



