EQUIPLANATION 



345 



and in most places support a considerable growth of a typically arctic 

 vegetation. The contacts between these flat or nearly flat stretches and 

 the residual masses are invariably abrupt, the residuals presenting to the 

 debris areas rock fronts often nearly perpendicular and ranging from 2 

 to 50 feet, but generally only from 3 to 10 feet in height (plate 18, fig- 

 ure 2). The often nearly flat or but gently inclined surfaces at the top 

 of these abrupt rock walls have, in places, a decidedly terrace-like appear- 

 ance (plate 18, figure 1). 



Upon investigating the relationships between the nearly flat surfaced 

 debris accumulations and the adjoining rock walls of the residuals it 

 was found that the limestones and dolomites are being slowly disinte- 

 grated, and to a considerable extent dissolved, to be later added to the 

 adjoining, generally frozen, superficial materials that fill the existing 

 bedrock depressions of the upland. By this process the accumulations 

 of debris are continually increasing at the expense of the rocky summits, 

 and thus the general plateau surface is becoming more and more plain- 

 like in contour. This process is here termed ^"equiplanation." 



DEFINITION 



The term equiplanation (L. aeqiius, equal; L. planus, plain) is in- 

 tended to include all physiographic processes which tend to reduce the 

 relief of a region and so cause the topography to eventually become more 

 and more plainlike in contour without involving any loss or gain of 

 material to the area affected — that is, the amount of material remains 

 apparently equal or is not increased or decreased by the plain-producing 

 process or processes. Material may be expected from certain districts 

 during the time equiplanation is in progress, but this export takes place 

 quite independent of the equiplanation. 



In the particular area along the Yukon-Alaska boundary line, de- 

 scribed in this paper, portions of the upland surface that are already 

 decidedly plainlike in character are becoming even' more so by the ero- 

 sion and disintegration of the residuals, and by the deposition of the 

 materials derived therefrom into the intervening bedrock depressions, 

 with the result that the general plateau surface is becoming more plain- 

 like in contour, without involving any perceptible loss or gain of material 

 to the areas affected. 



EQUIPLANATING PROCESSES 



In the area described the limestones and dolomites of the residual 

 masses of the upland, as previously mentioned, are being slowly disinte- 



