284 E. C. ANDREWS. 



gravitative form (an amphitheatre) induced when earth 

 materials fall evenly towards a vertical gash in the earth's 

 crust. 



Secondly, there is the corrasive action of the glacier as it 

 descends the slope of sapping. 



These basal and central actions then determine a double 

 slope for the cirque proper [Fig. 8 (d); Part I). 



A third but more gentle slope is doubtless formed fre- 

 quently by ordinary sapping methods at still higher levels, 

 where the snow mass is too small in volume to accomplish 

 much corrasion. 



This is of course on the assumption that the ice volume 

 has not diminished seriously during the recession of the 

 glacial valley head. On the other hand we have undoubted 

 proof that in all Alpine valleys known to us, the present 

 glaciers are but the dwarfed representatives of ice streams 

 which have but recently disappeared. So recent has been 

 this disappearance that the very scratches and "polish" 

 they left on the valley sides and bottoms have not yet been 

 obliterated by later erosive activities. Evidently then the 

 cirques as we see them to-day have been fashioned by the 

 recent ice streams, if by glaciers at all. Let us see then 

 whether any trustworthy information as to the formation 

 of cirques could be gained by an examination of the action 

 of the present glaciers in their cirques. Now the first 

 action of a dwarfed stream is to readjust its channel grade 

 so as to recommence the work of corrasion along a channel 

 adjusted to its own strength (See Parti of this Series). In 

 the particular case under consideration the first stage in 

 this readjustment process therefore is aggradation at the 

 s pots where the greatest local variation of ice velocity had 

 produced the most marked interruptions of channel grades. 

 The dwarfed glacier therefore will commence dumping 

 debris on the base of the cirque; the high walls of the 



