388 Jiemark'i on G lacier f. 



sioned by certain movements of the ice, for which it is diffi- 

 cult to account. They might he called the cuts of a chisel in 

 the flat surface of the rock. 



Particles of the hardest sand, which are always found be- 

 tween the ice and the rock, such as small crystals of (juartz, 

 ifcc, produce the same eflPect as so many diamonds, by form- 

 ing lines on these polished surfaces, which are thus covered 

 with a multitude of rectihnear strias parallel to each other. 

 These striae have no dependence on the structure of the rock ; 

 they do not follow its cleavage ; they are seen to cut in two 

 the crystals they traverse : they are always in lines of great 

 inclination, and follow the direction ^^•hich the fonn of the 

 subjacent ground has given to the ice, whether in its regular 

 progi-ess or accidental deviations. They cannot be attributed 

 therefore, as has been done by Deluc, to rapid currents of 

 water, nor to muddy currents filled with fragments of rocks, 

 as some other observers are inclined to believe. The debacle 

 of the Dent du Midi, which presented a fine example of a cur- 

 rent of this natm-e, has not left any trace of this kind in any 

 part of its course. 



Fmally, we perceive, on surfaces which the ice has left, 

 other furrows, not rectilinear but undulated, often nmning 

 into each other, and generally following the Une of the gi'eatest 

 declivity. These are called Carrenfelder in some parts of the 

 Alps. These fiuTOws are evidently owing to the erosion of 

 waters circulating beneath the glace, and gradually scooping 

 out a bed down the dechvity. Other erosions are likewise 

 observed, exactly resembling those produced by a cascade in 

 the place where it falls, and which probably have no other 

 origin. 



All these actions of the ice are somewhat modified by the 

 nature of the rock on which they are exercised. Granite be- 

 comes rounded in large masses, and broad convex surfaces of 

 a pretty uniform description. The masses in limestone are 

 smaller, and acquii*e the most perfect polish. It alone pre- 

 sents beautiful surfaces, resembling those of a slab of marble 

 from the hands of the workman. Gneiss and the schists 

 are more fuiTowed, although often in a direction transverse to 

 their beds. 



