Cairnes — Some Suggested New Physiographic Terms. 77 



remain apparently equal, or are not increased or decreased by 

 the plain-producing process or processes. Material may be 

 exported from certain districts during the time equiplanation 

 is in progress, but this export takes place quite independent of 

 the equiplanating. 



Deplanation (L. de, from ; L. planus, a plain) includes all 

 physiographic processes which tend to reduce the relief of a 

 district, and so cause the topography eventually to become 

 more and more plain-like in contour, dominantly by subtract- 

 ing material from the area or areas affected. 



Applanation (L. ad to or upon ; L. plamis, a plain) in- 

 cludes all physiographic processes which tend to produce 

 land-forms having plain-like surfaces, or tend to reduce the 

 relief of a district and so cause the topography eventually to 

 become more and more plain-like in contour, dominantly by 

 adding material to the area or areas affected. 



Classification of Physiographic Processes. 



All physiographic processes, forces, or agencies that tend to 

 alter the topography of a district by reducing the relief and so 

 eventually cause the surface to become more plain-like in con- 

 tour, may thus be considered as deplanating, applanating, or 

 equiplanating in character, depending upon whether their 

 activities result dominantly in a loss, a gain, or neither loss 

 nor gain, respectively, of material, within the areas affected. 

 Many processes or forces, however, such as certain forms of 

 volcanic activity and some phases of diastrophism, instead of 

 producing plain-like surfaces, tend primarily to destroy them. 

 All physiographic processes, that do not tend ultimately to 

 reduce the relief of the region in which they are engaged, may 

 thus be regarded as " nonplanating." It is thought that it may 

 be conducive to a clearer understanding of various physio- 

 graphic processes, if each be considered under the division of 

 this suggested classification to which it belongs. Normal 

 stream action, for instance, has a deplanating effect, but in dis- 

 tricts having interior drainage, the results of stream action are 

 to produce equiplanation. Similarly, wind action may be 

 either deplanating, applanating, or equiplanating. Frost action 

 may be strongly deplanating in character, or may be an impor- 

 tant factor in causing equiplanation. 



Most modern writers in describing plain-like surfaces, which 

 here include both plains and plateaus, consider these all to 

 belong to one of two main genetic types. For example, 

 Geikie* classifies plains as : 



*Geikie, James, " Earth sculpture," pp. 335-339,1898. 



