324 PROCEEDINGS OP THE GEOLOGICAL SOCIETY. [Apr. 5, 



to be solved with, the means at present at our disposal ; my own 

 belief, after many years of observation, is, that subterranean forces 

 (whether of upheaval or depression, by folding and fracturing the 

 strata), sea, air, frost, rain, streams, and glaciers have all played 

 their part in this task of mountain-sculpture. Perhaps it may be 

 possible some day to approximate to the work done by the first 

 two ; but the more I examine the Alps the more convinced I become 

 that the next four have been the cbief agents in producing the pre- 

 sent configuration of their valleys, and that the eifect of the last in 

 the list has been superficial. Earth-forces, like Titanic hands, have 

 moulded and broken, the sea has planed, the heat and cold have 

 split like wedges, rain and rivers have chiseled and sawn, while the 

 glacier rasp has rounded edges and filed down protuberances, but 

 has done comparatively little among the harder rocks to deepen or 

 excavate. 



[P.S. Since the above 'paper was read, Mr. E. "Whymper's ' Scram- 

 bles amongst the Alps ' bas been published, in which are some very 

 important remarks upon the question of glacier-erosion. Professor 

 Tyndall, in his recent work ' Hours of Exercise in the Alps,' appears 

 to speak rather less confidently with regard to his theory than in 

 the paper quoted above.] 



Discussion. 



Mr. Whitakee suggested an analogy between the cirques and the 

 combes in our own limestone countries. 



Mr. Geikie regarded the cirques as analogous to the cwms of 

 Wales and the corries of Scotland. They were not, however, con- 

 fined to limestone districts, but occurred also in gneiss and granite 

 rocks. He thought that the shape was much infiuenced by the bed- 

 ding and jointing of the rocks, as there was an evident connexion 

 between these and the shape of the cwms. He could not, however, 

 see his way to account for the vertical cliff's surrounding the cirques. 



The Eev. T. G. Bonnet, in reply, observed that though cirques 

 were not confined to limestones, the finest instances occurred in such 

 rocks. When cirques occurred in crystalline rocks, the talus was 

 usually much larger than in limestone. 



