1846.] HOW BLOCKS ARRIVE ON THE SURFACE OF GLACIERS. 203 



stones are actually extruded, although in a peculiar manner, 

 from pure ice, or at least exposed by the ablation of the surface. 



In my Travels, p. 241, referring to the excessively gradual 

 development of the moraine of La Noire on the Mer de 

 Glace of Chamouni, I stated my belief, that this moraine was 

 buried in a fold between two glaciers, one of which had over- 

 flowed the other, and that, as the upper glacier decayed away, 

 the rocky fragments were strewed on the surface. A fresh ex- 

 amination of the same localities leaves me in the same want of 

 direct proof of this fact, but the difficulty of explaining it other- 

 wise, makes me suppose my former view correct. 



The extruded stones on the Glacier du Nant Blanc, near 

 Chamouni (alluded to in the first part of this letter), present a 

 very remarkable appearance, imperfectly shown in Plate VIII. 

 fig. 6. The right bank of this glacier (that which appears on 

 the left of the figure as seen from a distance) is at first bounded 

 by rocky summits, but in the lower part of its course by a 

 mound-like moraine of the usual form. The surface-blocks can 

 only be derived from the precipices near the origin. Yet they 

 do not even appear on the surface opposite to the rocks, but 

 only opposite to the moraine ; and they increase in number and 

 quantity towards the lower end of the glacier, where they 

 almost blacken the surface of the right side, the left side remaining 

 almost clean. It is difficult to believe that this accumulation is 

 not due to the gradual denudation of the blocks by the melting 

 of the ice in which they have been, in some way or other, im- 

 bedded ; but it is scarcely less difficult to admit that, having 

 fallen from the rocks above the Neve, they should have remained 

 unperceived in the ice during all the intermediate space. 



To take another example. The glacier of the Rhone is 

 distinguished by the extraordinary purity of its surface, and the 

 consequent absence of lateral moraines. But this general free- 

 dom from stones on the surface is subject to one exception, 

 which is remarkable : Stones begin to appear at the surface on 

 the terminal slope at a considerable height. How came they 

 there ? Not a stone the size of the fist can be seen on the sur- 



