S-i Cairnes — Some Suggested New Physiographic Terms. 



drainage, as shown previously, all physiographic agencies, 

 including stream-action, wind, and weathering forces, have 

 eqnipianating tendencies ; in addition to assisting equi- 

 planation, by depositing over the lowlands material eroded 

 from the surrounding and included residual highlands, the 

 wind also exports vast amounts of fine dust to neighboring 

 regions. In so far as the desert tracts are made more plain- 

 like by the removal of exported, wind-home material, this 

 process is deplanating, and may hecome effective in the mature 

 and old stages of an arid cycle. However, instead of smooth- 

 ing the surfaces of desert lands, the wind more frequently has 

 a roughening effect. So extensive, in fact, is this process that 

 the drainage which, during the late mature stage of an arid 

 cycle, tends to be reduced to a completely integrated con- 

 dition, becomes during the later stages again disintegrated 

 largely by the production of wind-blown hollows. The plain- 

 producing forces in regions having interior drainage are thus 

 regarded as being dominantly eqnipianating in character. In 

 areas having exterior drainage, the wind is a true deplanating 

 agent and produces its quota of fines, which is added to that 

 resulting from the other destructive physiographic agencies, 

 and eventually commences its stream-borne journey toward 

 the ocean. The deplanating activities of the sea arid of 

 inland-ice are outlined in later paragraphs. 



Probably much the most extensive of the surfaces produced 

 by deplanation are those generally considered to be uplifted 

 peneplains. Peneplains and plains of marine denudation may 

 be readily distinguished from glacial plains or plains produced 

 by inland-ice,* but between the first two there is greater 

 similarity. 



In certain regions, also, there is considerable uncertainty as 

 to whether planation is due to normal erosion (peneplanation) 

 or was produced during an arid climate and under interior 

 drainage conditions, and hence without reference to sea-level. 

 It is difficult to prove, for instance, that the streams traversing 

 the Arizona plateau had exterior drainage, during the time the 

 region was being planated, and until this can be demonstrated, 

 the elevation of this tract during the time of the denudation 

 must remain uncertain. 



It would, therefore, seem convenient to employ the term 

 deplanation to include all processes, forces, agents, etc., which 

 tend to reduce the relief of any region in which they are 

 active, by the removal of material therefrom, regardless as to 

 the nature or ultimate result of these activities. 



* The term inland-ice is here employed to include ice-sheets or continental 

 glaciers as contrasted with mountain or valley glaciers. See :— Hobbs, W. 

 H., "Characteristics of existing glaciers," 1911, pp. 97, 98. 



