316 PHOCEEDINGS OP THE GEOLOGICAL SOCIETY. [Apr. 5, 



(1.) I dismiss at once any theory of " craters of upheaval," by 

 which some distinguished geologists have attempted to account for 

 valleys which approach the cirque form, such as that of La Berarde*, 

 because, after examination of this and many others, I can conceive of 

 no theory of upheaval or fracture which could leave them in a state 

 at all resembling their present one. That a vaUey like the one at 

 La Berarde, to say nothing of these cirques, should be a " crater of 

 elevation ' appears to me a physical impossibility. 



(2.) Can these cirques be explained by any theory of marine 

 erosion, and compared with the coves which we not unfrequently find 

 on the sea-coast ? Though possibly this explanation might be applied 

 to some cases, I do not think it will fit all or nearly aU that exist. 

 After seeing how little efiect the sea has in the Fjords of Norway, 

 I cannot attribute the Fer-a-Cheval or the Creux de Champs in these 

 remote and sheltered valleys to marine erosion, whatever effect the 

 waves may once have had in blocking out the main features of the 

 Alpine peaks f. 



(3.) Can we call in the intervention of glaciers, now so muct in 

 favour as nature's carving-tools among geologists ? and may these 

 cirques be regarded as results of what Mr. Euskin would caU " minor 

 fury of ice-foam " J ? We shall perhaps best answer the question by 

 considering first this particular case : — whether, assuming that glaciers 

 have been principal agents in the excavation of Alpine vaUeys, we 

 can suppose the cirques to have been formed by them ; and second, 

 whether the assumption just made, that glaciers have been principal 

 agents in the excavation of Alpine valleys, is a correct one. Now, 

 if these cirques are the result of glacial erosion, they were either 

 fashioned (a) by a glacier which took its rise in them, or (6), like the 

 concavities in the course of a river, by the action of a passing ice- 

 stream. The first of these suppositions appears to me physically 

 impossible. Granting, as we must do, to begin with, some kind of 

 hollow or slight combe on the mountain-side in which the snows 

 could coUect and form a neve, the erosive action on this part would 

 always be very slight (for the ice here is less compact than that below) ; 

 the friction would be that due to the weight alone of the superin- 

 cumbent ice II, and, what is most important, there is but little grit 

 between it and the subjacent rock ; for comparatively few stones are 

 engulfed in the neve of a glacier. I can conceive it possible that if 

 a glacier, after wearing away a stratum of hard rock, reached one 

 in which erosion proceeded more rapidly, it might deepen its angle 

 of descent to some degree in the upper stratum also ; but I cannot 

 conceive that precipices more than a thousand feet high could be thus 



* In Dauphin^. See Forbes's ' Norway and its Glaciers,' p. 259. 



t My own examination of mountains has led me to conclusions very different 

 from those advocated by Mr. Mackintosh in his 'Scenery and Greology of England 

 and Wales,' although I think it possible that some peaks and ranges may have 

 originated in insular fragments. 



X Geol. Mag. vol. ii. p. 50. 



II Friction OC normal pressure ; in many of the lower parts of a glacier, 

 normal pressure at any point = weight of column of ice above that point + a 

 pressure derived from ice behind. 



