BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 VOL. 33, PP. 587-598 SEPTEMBER 30, 1922 



PENEPLAINS AND THE GEOGRAPHICAL CYCLE 1 



BY W. M. DAVIS 



{Presented before the Society December 29, 1921) 



CONTENTS 



Page 



General features of a peneplain 587 



Subsequent streams and valleys 589 



The geographical cycle and its complications 590 



Climatic changes during a cycle of erosion 591 



Misconception of the geographical cycle as a rigid scheme 593 



Essential features of the geographical cycle 594 



Induction and deduction in the scheme of the cycle 595 



Deduction in the scheme of the arid cycle 596 



Unlike use of the cycle in geology and geography 597 



General Features of a Peneplain 



If a landmass of whatever structure and large area be upheaved un- 

 equally to considerable altitudes in its interior area and if it then stand 

 still for an indefinitely long period, it will be eventually degraded to 

 a plain. In order to avoid the necessity of assuming so indefinitely 

 long a period of still-stand, and in order at the same time to detain 

 attention upon the gently undulating surface that such a region will have 

 before it is worn down to a plain, the term peneplain was invented some 

 thirty years ago. As no one, I believe, proposes to call the surface of 

 ultimate degradation a "plane," I see no sufficient reason for calling the 

 penultimate surface a "peneplane," as some have proposed; the original 

 spelling, peneplain, is preferred. 



When the term was first proposed it was vaguely defined; and it has 

 recently come to my knowledge that the vagueness of its definition has 

 led some students of the physiographic evolution of the Appalachians to 

 make for themselves a fuller definition, which I hope they will publish. 

 In the meantime the following statement is offered of my own views 

 upon the subject, as they have been gradually developed during the 



1 Manuscript received by the Secretary of the Society January 24, 1922. 



XXXIX — Bull. Geol. Soc. Am., Vol. 33, 1921 (587) 



