8 president's address. 



afterwards inevitably combined as the hollow widened and deepened.' 

 Each of the great cirques is still a 'land of streams,' and they are 

 kept permanent for the greater part of the year by beds of snow on the 

 ledges above its walls. 



The ' sapping and plucking ' process presents another difficulty — 

 the steps already mentioned in the floors of valleys. These are sup- 

 posed to indicate stages at which the excavating glacier transferred its 

 operations to a higher level. But, if so, the outermost one must be 

 the oldest, or the glacier must have been first formed in the lowest part 

 of the incipient valley. Yet, with a falling temperature, the reverse 

 would happen, for otherwise the snow must act as a protective mantle 

 to the mature pre-glacial surface almost down to its base. However 

 much age might have smoothed away youthful angularities, it would 

 be strange if no receptacles had been left higher up to initiate the 

 process; and even if sapping had only modified the form of an older 

 valley, it could not have cut the steps unless it had begun its work 

 on the lowest one. Thus, in the case of the Creux de Champ, if we 

 hesitate to assume that the sapping process began at the mouth of 

 the valley of the Grande Eau above Aigle, we must suppose it to have 

 started somewhere near Ormont Dessus and to have excavated that 

 gigantic hollow, the floor of which lies full 6,000 feet below the 

 culminating crags of the Diablerets. 



But even if ' sapping and plucking ' were assigned a comparatively 

 unimportant position in the cutting out of cirques and corries, it might 

 still be maintained that the glaciers of the Ice Age had greatly deepened 

 the valleys of mountain regions. That view is adopted by Professors 

 Penck and Bruckner in their work on the glaciation of the Alps, 1 the 

 value of which even those who cannot accept some of their conclusions 

 will thankfully admit. On one point all parties agree — that a 

 valley cut by a fairly rapid stream in a durable rock is V-like in section. 

 With an increase of speed the walls become more vertical; with a 

 diminution the valley widens and has a flatter bed, over which the river, 

 as the base-line is approached, may at last meander. Lateral streams will 

 plough into the slopes, and may be numerous enough to convert them into 

 alternating ridges and furrows. If a valley has been excavated in thick 

 horizontal beds of rock varying in hardness, such as limestones and 

 shales, its sides exhibit a succession of terrace walls and shelving banks, 

 while a marked dip and other dominant structures produce their own 

 modifications. It is also agreed that a valley excavated or greatly 

 enlarged by a glacier should be U-like in section. But an Alpine 

 valley, especially as we approach its head, very commonly takes the 

 following form : For some hundreds of feet up from the torrent it is 



1 Die Alpen in EiszeUnUcr (1909). 



