THE TWIN LAKES GLACIATED AREA 307 



were largely from this same area. These things suggest strongly 

 that the material removed from the valley during the earlier period 

 of glaciation was as great, and probably greater, in amount than that 

 removed during the later glaciation. The question naturally rises: 

 Is it possible to detect in the rock valley of Lake Creek evidence of 

 these two glaciations, which we know must have occurred ? It is 

 not easy, since the work of the later period would continue that of 

 the earlier, and all products of erosion would be removed from the 

 valley. But it is thought that evidence in favor of two periods of 

 glacial erosion, with the larger amount of work done in the earlier 

 period, is found in the relation of the hanging valleys to the main 

 valley. 



In typical hanging valleys the contours of the lower slopes of the 

 main valley continue unchanged beneath the hanging valley. A 



Fig. 11. — Profile of hanging valley. 



cross-section of the main valley and long profile of the lateral hanging 

 valley is given in Fig. 11, in which AB is the longitudinal profile 

 of the hanging valley. But the profile of the typical hanging valley 

 of the Twin Lakes region would be represented by AECD, the 

 triangle ECB representing a narrower or broader notch which has 

 been cut out from the side of the general valley immediately below 

 the hanging valley. Such a re-entrant could conceivably be cut 

 out by the main glacier, or by the lateral stream. There seems to 

 be no good reason why the ice should favor the side wall beneath 

 the hanging valleys generally, and in some cases these cuts are too 

 sharply re-entrant for ice-work. Further, these notches contain in 

 almost all cases morainic material; and this is the case whether 

 the lateral valleys were occupied by ice or not. They are areas of 

 glacial deposit rather than of erosion. Their origin seems to be as 

 follows: During the earlier period of glaciation the main glacier 

 cut its valleys below the level of the tributary valleys, producing nor- 

 mal hanging valleys, the longer of which were occupied by tributary 



