condition of a crystalline solid. Therefore upon a consider- 

 able reduction in glacial volume, the old flood channel of 

 the ice will be altogether too large for it, and it will be 

 placed in a condition of tension in its attempts to accom- 

 modate itself to the channel profiles. Especially will this 

 be the case at the points of maximum interruption of the 

 channel base, such as the huge cutting curves of the Ice 

 Flood, the broad channel floors and in the basins lying along 

 the old glacial thalweg. This tension will be expressed 

 as crevasses, because at the points just enumerated, 

 there will be a minimum of pressure under the ice drought 

 conditions as opposed to the maximum of pressure under 

 the Ice Flood conditions. One would then expect berg- 

 schrunds or crevasses to occur at various distinct varia- 

 tions in channel slope. Furthermore there would be a 

 tendency for the glacier at sucli points to be convex near 

 the centre of the stream, whereas in the Ice Flood the 

 tendency above the cirque foot was to sag by reason of 

 increased mobility and velocity, and to heap itself towards 

 the sides at points a little lower down and nearer the lower 

 portion of the cirque. 



Again the tendency of all reduced streams is first to 

 aggrade all the larger irregularities of the channel base, 

 and then this having been done to cut smaller channels 

 along the base of the old and larger channel formed by the 

 flood stream. 



Applied to the cirque and down stream "tread" and 

 "step," this shows that the early action of the reduced 

 glaciers is to fill the basins with debris, by reduction of the 

 vertical measure of corrasive strength, and secondly to 

 forsake the old wide cutting curves and crowd towards the 

 centre or deepest portion of the flood channel and deposit 

 moraines (Fig. 15) in the cutting curves during the 

 process. 



