92 /. G. ANDERSSON 



the erosive system is highly supported in its work by the weathering 

 of the rock and by a slow movement of the waste-sheet down the slopes 

 The latter process, generally little estimated, has been clearly 

 sketched by the master of the American "base-levehng" school, 

 W. M. Davis: 



The movement of land-waste is generally so slow that it is not noticed. 

 But when one has learned that many land forms result from this removal of 

 more or less waste, the reality and the importance of the movement are better 

 understood. It is then possible to picture in the imagination a slow wasting 

 and creeping of the waste down the land slopes; not bodily or hastily, but grain 

 by grain, inch by inch; yet so patiently that in the course of ages even moun- 

 tains may be laid low Every change of condition between cold and warm, 



dry and wet, melted and frozen, that causes a gain or a loss of volume in the 

 rock -waste aids its slow movement down-hill. With countless minute changes 

 every particle is led, slowly but surely, from higher to lower ground.^ 



It seems to me that it is in the removal of the waste, by which 

 the undecayed rock is again exposed to the attack of the weather 

 and the debris is carried to the primal streamlets, that this process, 

 in its more or less rich development, chiefly determines the effect- 

 iveness of river-action in peneplaining. Professor Davis supposes 

 that the removal of the waste may continue also underneath a cover 

 of vegetation, and he points out that "the growth and decay of 

 plant roots aid the downward creeping of the waste." But expe- 

 rience has taught us that in regions covered by a rich vegetation 

 the removal of the debris must be very slow, as the unaltered rock 

 is, in most cases, hidden by a deep covering of decayed material. 

 In those lands where the climatic conditions are unfavorable for 

 the removal of the waste the material carried away by river transport 

 must be comparatively scarce and the subaerial denudation only 

 very slow in its advance toward its final end, the peneplain. 



But, on the contrary, in regions where the vegetation, because 

 of the hostility of the chmate, is all too scarce to fix the detritus, 

 but when the precipitation is still abundant enough to cause effective 

 action by running water, a quick removal of the waste and a plen- 

 teous feeding of the streamlets with detritus highly accelerate the 

 subaerial denudation. 



During the last few years I have had opportunity of studying, 



I Davis, Physical Geography, pp. 263, 267. 



