152 Professor Forbes's Thirteenth Letter on Glaciers. 



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 examination of the same localities leaves me in the 

 same want of direct proof of this fact, but the difficulty of 

 explaining it otherwise, 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 shewn in Plate II., 

 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 num- 

 ber 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 

 accumulatiom 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, imbedded, 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 Ehone is 

 distinguished by the extraordinary purity of its surface, and 

 the consequent absence of lateral moraines. But this gene- 

 ral freedom from stones on the surface is subject to one ex- 

 ception, which is remarkable : — Stones begin to apipear 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 surface farther up ; and, in examining a num- 

 ber of the crevasses, I could not see any engorged in the 

 ice. The explanation seems to be that the stones are 

 actually introduced into the ice by friction at the bottom 

 of the glacier, and forced upwards by the action of the 

 frontal resistance which produces \kiQ frontal dip of the veined 



