path of a particle that the maximum percentage of stream 

 energy is expended at the points where the plane of the 

 thalweg most opposes the motion of the stream, that is 

 where the planes of thalweg and descending stream are 

 inclined at the least angle to each other. 



Thus in figure 8 the greatest percentage of the stream 

 strength expended as corrasion will be at B, A and B', 

 because here the planes of thalweg and stream are inclined 

 together at less angles than at any other points along the 

 thalweg. For the same reason the least percentage of 

 stream strength expended as corrasion occurs along the 

 slopes O B and 0' B' because at these points the planes of 

 thalweg and stream tend to parallelism. The points need- 

 ing consideration are the relative values of corrasion at 

 the points A and B. During it* descent of the slope O' B' 

 the stream has heen increasing rapidly in kinetic energy, 

 while at the same time at A it has been robbed of a great 

 portion of its energy in the formation of the basin B A. 

 Therefore at the point B' where the plane of the thalweg 

 opposes the motion of the stream, the actual amount of 

 corrasive strength exerted far exceeds that exerted at the 

 point A. The action at B' is to produce a basin or to over- 

 deepen its channel so as to produce a decided interruption 

 Of the channel base because the energy expended at this 

 spot far exceeds the energy expended as corrasion at any 

 other point along: the thalweg. A strong sapping action is 



the atmospheric slope of repose, but this slope in turn is 

 completely modified by the action of the stream in passing 

 down the slope O' B'. 



It will be advisable to discuss this action a little more in 

 detail as the former "paradox .,i' giaeia! erosion" was due 

 0) to the failure to grasp the tendency of a stream to 

 parabolic motion, and (2) to the failure to appreciate the 



