302 E. C. ANDREWS. 



may be expected to carry basins of but relatively slight 

 depth. If the "step" recession be very pronounced and 

 very rapid, the "tread" may not even possess a basin, its 

 general profde being that of a gentle slope from "step" to 

 "step." To return to the recession of the "step" at Bin 

 Fig. 14 (a). It will be carried back right into the divide 

 at A. Nevertheless the "step" at A (the glacial divide) 

 will differ in some important points from the "steps" at D 

 and C. In the case of the latter the sapping action of the 

 heavy glacial motion is very pronounced, and with this 

 must be combined the quarrying action of the glacier as it 

 descends the whole of the profiles OC, E E'. This results 

 in the wholesale smashing up of the structures forming 

 these profiles, and in these incipient or recessional stages, 

 the most youthful forms of glacial corrasion may be 

 expected, such as V-shaped rectangular or irregularly- 

 shaped cross-sections, there being but little opportunity 

 for the development of symmetrical forms. 



But in the case of the cirque proper, which has been 

 developed at or very close to a glacial divide, the action is 

 such as to produce a very different profile to that of the 

 typical "step." We have seen that the typical cirque 

 commences as a small "step" which by recession passes 

 into the typical cirque at the glacial divide. Such action 

 may occur along all the tributaries as well as along the 

 main glacial valley itself ; but in each case the action is 

 similar. In the case of the main valley one would expect 

 to ascend the thalweg by means of a series of "steps" and 

 "treads," the highest tread ending in a cirque instead of 

 an ordinary valley "step." In the case of a tributary 

 valley one would rise up to it from the main valley by 

 means of a "step," thence its floor would ascend in much 

 the same fashion as that of the main valley. Thus one 

 would expect to see tributary cirques discharging into the 



