Cairnes — Some Suggested New Physiographic Terms. 79 



tendency is for this elevated surface to become gradually more 

 and more plain-like in contour, without experiencing any 

 regional loss or gain of material. 



A prolonged rise of temperature, however, would thaw the 

 accumulations of debris on the upland, and would result in the 

 greater amount, at least, of this material being rapidly removed 

 by water action to the main valleys. 



While equiplanation is engaged in planating the upland, 

 normal erosion is slowly destroying the remaining portions of 



Fig. 1. 



Fig. 1. General view of the dissected upland surface of the Yukon pla- 

 teau along the 141st meridian (the Yukon-Alaska International boundary) at 

 north latitude 66° 50'. This upland has an average elevation of about 3,500 

 feet above sea-level. 



this surface by more completely dissecting it, and by widening 

 the intersecting drainage depressions and causing the valley- 

 walls of neighboring streams to gradually approach one 

 another. 



The equiplanating process here described is not thought to 

 be limited to the particular district under consideration, but is 

 believed to be more or less active throughout extensive areas 

 subjected to an arctic climate. Since, however, these areas 

 have been but little explored, the phenomenon has not been 

 described. 



