CORRASION BY GRAVITY STREAMS. 285 



cirque will sliower debris on to the glacier, and the glacier 

 itself will tend to stagnate in the basal portions of the 

 valley, possibly even preserving a banded appearance to its 

 very front. Around the upper portion of the glacier the 

 ice will now not be moulded to the wall, owing to this new 

 relation existing between the diminished glacier and the 

 wall which had been adjusted to the strength of the older 

 and much larger glacier. Cracks curving sympathetically 

 with the wall of the cirque now indicate this ill-adjustment 

 of ice and old channel form, this straining of the dwarfed 

 stream mass to fit itself to the too generous porportions of 

 the containing amphitheatre. In the earlier stages when 

 the channel profiles were formed by the stream, there 

 were few or no crevasses and no bergschrunds, for then 

 the depth and strength of the ice were so adjusted as to 

 make it a true stream, whose surface was continuous over 

 any interruptions of channel base other than great ice falls, 

 [that is, where valley heads were receding along valley 

 floors]. But now during the dwarfed or drought stage the 

 surface of the glacier is not deep and large enough so as to 

 give the plasticity requisite to maintain a continuous sur- 

 face while traversing the monstrous interruptions of grade 

 formed during the earlier or flood stage. Nevertheless 

 the ice is forced to accommodate itself to the irregularities 

 of the channel base, since all streams must follow the 

 thalweg ; it is therefore in a state of perpetual tension and 

 the crevasses express its attempts at adjustment of glacial 

 surface to basal movement. Fill up the cirque and associ- 

 ated valley to the old ice level and we have a stream with 

 surface harmoniously continuous as a result of perfect 

 adjustment of glacial strength to channel profiles. Such a 

 glacier would be practically free from crevasses. When 

 this readjustment process is complete, the diminished ice 



I stream will commence excavating smaller cirques and 



