Ancient Extent of the Glaciers of Chamonix. 63 



emery composed of pebbles or sand derived from harder 

 rocks, such as gneiss, granite, or protogine, the striae will be 

 very strong marked. This may be observed at the foot of 

 the glaciers of Rosenlaui and Grindelwald, in the Canton 

 of Berne. On the contrary, if the rock be gneiss, granite, 

 or serpentine, that is to say, very hard, the striae will be 

 shallower and less marked, as may be observed in the glaciers 

 of the Aar, Zermatt, and Chamonix. The polish will be the 

 same in both cases ; and it is often as perfect as that of the 

 marbles which ornament our buildings. 



The stride engraved on the rocks containing these glaciers, 

 are in general horizontal or parallel to the surface ; but at the 

 narrowing of the valleys these stride rise and approach the 

 vertical. We need not be surprised at this. Forced to make 

 its way through a narrow pass, the glacier rises at the sides, 

 and ascends along the flanks of the mountains which obstruct 

 its progress. This is admirably witnessed near the Chalets 

 of Stieregg, a narrow defile through which the lower glacier 

 of Grindelwald is obliged to force its way, before it spreads 

 itself in the valley of the same name. On the right bank of 

 this glacier, the striae are inclined 45° to the horizon ; on the 

 left bank, it rises sometimes to the neighbouring forests, and 

 drags along large banks of earth covered with tufts of rhodo- 

 dendron, elder, birch, and pines. The soft and foliated rocks 

 are bruised and broken in pieces by the prodigious force of 

 the glacier. The hard rocks resist it ; but these rocks also, 

 by their flattened, worn, polished, and striated surfaces, bear 

 testimony to the enormous pressure to which they have been 

 subjected. It is in this way that, in the glacier of the Aar, 

 the foot of the promontory on which M. Agassiz has erected 

 his pavilion, is polished to a great height ; and on the face 

 turned up the valley I observed striae incline 64°. The ice 

 rising against this encampment seems as if it would have 

 scaled it ; but the granite rock resisted, and the glacier was 

 obliged to turn slowly round it. 



In short, the considerable pressure of a glacier, joined to 

 its'progressive movement, acts at the same time on the bottom 

 and sides of the valley which it traverses. It polishes all the 

 rocks which afford sufficient resistance not to be destroyed by 



