1865.] SIR R. I. MURCHISON ON GLACIERS. 31 



excavating them. Also, the glacier of the Rhone, the principal part 

 of which can be so conveniently studied, advances on a gravelly 

 substratum, in which it does not form a channel. Such being the 

 facts as regards glaciers now advancing, M. Collomb cites equally 

 strong, if not still stronger, cases, in support of his view, as deriv- 

 ed from the observation of retiring or shrinking glaciers in the 

 valleys of the Alps. Examining last year with M. Daubree the 

 glaciers of the Valley of Chamounix, he was attracted to that 

 named Bossons, which he had not seen for five years. During 

 that time the glacier had shrunk very considerably, both in altitude 

 and length, and yet upon the surface of the ground from which it 

 had retired there was not the smallest sign of excavation. 



Viewing a glacier as a plastic body, we know that it is pressed 

 onwards by gravitation from the increasing and descending masses 

 of snow and ice behind it in the loftier mountains, and, being forced 

 to descend through narrow gorges, it naturally acts with the greater 

 energy on the precipitous rocky flanks of these openings ; striating 

 and polishing them with the sand, blocks, and pebbles which it 

 holds in its grasp. But, as before touched upon, the narrowness 

 of many of those channels through which glaciers have been thrust 

 for countless ages, is in itself a demonstration that the ice can have 

 done very little in widening the gorge through which it has been 

 forced, and where, of necessity, it exerted by far its greatest power. 

 In other words, the flanking rocks of each gorge have proved infi- 

 nitely more stubborn than the ice and its embedded stones, which 

 have merely served as gravers and polishers of the granites, quartz 

 rocks, porphyries, slates, marbles, or other hard rocks, among 

 which the frozen river has descended. And, if such'has been the 

 amount of influence of advancing glaciers in the higher regions, 

 where the body descends with the greatest power, how are we to 

 believe that when this creeping mass of ice arrived in low countries 

 (as for instance in the depressions occupied by the Lakes of Geneva 

 and Constance) it could have exerted a power infinitely greater 

 than that which it possessed in the higher regions? 



When we turn from modern glaciers to the remains of those of 

 ancient date, the proofs are equally decisive, that, whatever might 

 be their extent, those gigantic bodies exercised no excavating 

 power. I am reminded by M. Collomb, as well as by M. Escher 

 von der Linth, that in many parts of the Alps, vast old moraines 

 repose directly on incoherent and loose materials of quaternary 

 age ; the old drift of the Alps containing Elephas primigenius and 



