126 HARRY N. EATON 



reduction from the original peneplain; but he believes that the 

 stratigraphic sequence of the rock series in the Nittany valley 

 region must be taken into account in this connection. He lays 

 emphasis upon the fact that the Tuscarora is underlain by the 

 Juniata, a formation comparatively soft but not nearly as soft 

 as the Reedsville (Utica), which consists entirely of very fissile 

 shale. Thus the Oswego ridges would tend to become undermined 

 faster than those of the Tuscarora, and this fact, coupled with the 

 initial difference in weathering quality between the two sandstone 

 formations, would result in a consistent difference in height of the 

 ridge crests. 



Explanations of the present height of the lower ridges, involving 

 a process of reduction from former higher ridges, would seem risky 

 in view of the lengths to which such arguments can be carried. 

 Once admitting the possibility of the lower ridges maintaining 

 their even crests and owing their ultimate origin to differential 

 erosion, is it illogical to explain the even crests of the higher ridges 

 by gradual erosional development contemporaneous with and sub- 

 sequent to the long period of folding ? In short, arguing from the 

 topography of the ridges only, is it necessary to postulate a Cre- 

 taceous peneplain at all ? 



The writer has no alternative theory to suggest and no view to 

 advocate, but merely raises the question, feeling that the Cretaceous 

 peneplain theory does not explain adequately the existence of these 

 minor ridges. 



Of late the word "peneplain" has been used rather loosely and 

 has been applied to conditions where direct proof is lacking. It is 

 easy to conclude hastily that a ridge or series of ridges represents a* 

 peneplain, but much harder to prove such a statement. By no 

 means is every ridge or upland remnant the remains of a peneplain, 

 and a word of caution to workers in this field seems in order. 



Professor A. M. Miller^ may voice the feelings of others than 

 himself in the following words : 



.... when one examines the literature of modern physiography and sees 

 the readiness with which an "uplifted and dissected peneplain" is invoked 



' A. M. Miller, "Wind Gaps," Science, N.S., XLII, No. 1086 (October 22, 1915), 

 P- 573- 



