CORRASION BY GRAVITY STREAMS. 279 



increasing its velocity. This action in turn produces the 

 interruptions in the channel base which are expressed most 

 decidedly by basining. Such features are accentuated in 

 proportion as the time factor becomes important enough 

 to allow the flood glaciers to adjust the channel grade to 

 their strength. The disposition of tl>3 channel constrictions 

 or slopes or the arrangement of the confluent canons, when 

 forming a constriction at the point of confluence, will 

 determine which side of the main channel will be selected 

 for special attack by undercutting. [Fig. 5 (a), (b), (d), (e).] 



This is the analogy with the cutting curve of water and 

 of other streams. The seeming difficulty arising from a 

 comparison of the profiles formed by the various stream 

 types will be considered later. It may be mentioned iu 

 passing, that the difficulty is only apparent and not real, 

 and arises probably from a comparison of the action of one 

 stream type, when in the drought stage, with that of 

 another type when the latter is in the flood stage. 



But to return from this slight digression. If one channel 

 contains the larger and possibly more rapid glacier then by 

 composing the strength and direction of the larger with that 

 of the other but less important feeding stream, the direc- 

 tion of maximum glacial action will be found to lie along 

 the direction of the more important feeder rather than 

 along that of the less important one, (Fig. 5) and if this 

 confluence forms a channel constriction at the point of 

 junction, then the maximum stream action will form a 

 cutting curve in the constriction, and such cutting curve 

 will practically face the direction of motion of the stronger 

 glacial tributary. This will be the side also where basin 

 depths — if present at all — will be more pronounced and 

 where lateral cutting will be most emphasised. 



Now if a relatively small glacier discharges into the main 

 channel along this cutting curve its mouth will be made 



