7t> ( 'airnea — Some Suggested New Physiographic Terms. 



formity,* topographic adjustment,* superimposed youth,* and 

 solifluction.f All these have not only proved particularly con- 

 venient, hut have given us more clear-cut conceptions and have 

 also had a decided influence in promoting closer field observa- 

 tions. 



The suggestion of the definite name peneplain hy Prof. 

 Davis in 1889 for a thing previously considered in a general 

 way for a number of years, vastly promoted its consideration, 

 and greatly stimulated physiographic research. Investigations, 

 discussions, and writings followed rapidly after the christening 

 of the peneplain idea. 



At the annual meeting of the Geological Society of America 

 in Washington, D. C, during December, 1911, the writer pro- 

 posed the term equiplanation;}; to include certain physiographic 

 processes. Since that time a considerable number of inquiries, 

 concerning this subject, have been received. As a consequence 

 of the nature of these inquiries it has seemed advisable to write 

 this essay, which is intended to be somewhat in the nature of a 

 supplement to the original. In addition to containing some 

 additional data concerning equiplanation, two companion 

 terms "applanation," and "deplanation" are also suggested in 

 the hope of presenting in a more definite and comprehensive 

 manner certain points concerning the various plain-forming 

 processes and the more important forces and agents they 

 involve. It is, of course, not anticipated that these names will 

 prove of the same importance as those above mentioned, but it 

 is hoped that they also may serve a useful purpose. 



In the preparation of this paper, the writer has been very 

 kindly advised by Professor Isaiah Bowman of Yale University, 

 to whom he wishes to express his sincere gratitude. 



Definitions of Terms. 



Before defining deplanation and applanation, it is thought 

 advisable again to define equiplanation, in order that the rela- 

 tive significance of the three companion terms may be the 

 more apparent. 



Equiplanation (L. aequus, equal ; L. planus, a plain) 

 includes all physiographic processes which tend to reduce the 

 relief of a region and so cause the topography eventually to 

 become more and more plain-like in contour, without involving 

 any loss or gain of material, i. e., the amounts of material 



* Salisbury, E. D., " Three new physiographic terms," Jour, of Geol., vol. 

 xii, 1904, pp. 707-715. 



f Andersson, J. G., " Solifluction — a component of siibaerial denudation, " 

 Jour, of Geology, vol. xiv, 1906, pp. 91-112. 



X The title of the paper read was: "Differential erosion and equiplana- 

 tion in portions of Yukon and Alaska." 



