,,M ,„. Glaciers qfthe ^^/>*.,0RP',i)1'l ^ 



the mountains and the glaciers which cover them; if, in par- 

 ticular, wc consider the disappearance under the ice of certain 

 formations or strata of rocks, and their reappearance in other 

 places ; if we attend to the course of the acclivity of the valleys 

 from the extremity of a glacier to its commencement, &c. ; we 

 obtain the following conclusions : — The mean thickness of th^ 

 glaciers of the second kind, which descend into the inferior^y»|^^ 

 leys, is from 80 to 100 feet :* the thickness of those glacier$^^ 

 which are more elevated, and which fill the deeper valleys, may^ 

 be considered as ranging from 100 to 180 feet. The glaciers^ 

 of the first kind, which cover the summits, or extend over the , 

 declivities, scarcely attain 40 feet in thickness. Doubtless, there , 

 are deep holes in the rocks, where the thickness of the ice;, ^8 

 much more considerable ; the thickness likewise diminishes at 

 the limits of its extent. Bes'des, it is often formed after ava- 

 lanches in extraordinary heaps in certain places. In like manner, • 

 a winter very abundant in snow may augment, for a short tim^, 

 the thickness of the covering of the peaks.'^ 



*' The ice of a glacier of the second Tilndy is almost as hard 

 as rocks ; the sun, the rain, and the warm winds, ^ligh^ly ipell^ 

 its surface, but never soften the mass. If we travel on one of 

 these glaciers, even to more elevated regions, we see it, at a 

 height of about 7600 feet above the level of the se^, pass rapid-* 

 ly into the condition of ice of the first kind. It is composed of 

 round grains, about the size of a pea; the sun softens it to sucl|, 

 a degree, that we often sink in it to the knees ; but a moderate 

 cold restores it to its former hardness. The line of separation; 

 of the glaciers of the two kinds, is no other than the limit of 

 perpetual snow, that is to say, the height above which snow does 

 not melt in summer. It is customary to place this limit in ourj 

 mountains between 6000 and 9000 feet ; but if we consider 

 more accurately the melting of the snow, we shall be obliged Iq 

 assign to this hmit a much greater range. It does pfii ^p^ 

 that they have sufficiently distinguished, in this determinaliop^ 

 each of the two kinds of glaciers, and the snow properly 39 

 called ; they, have not observed correctly the diiTerept manner 



* De Saussure obtained precisely the same result at the ghcier of Bitf( 

 but he thinks that accidentally he met with much thicker ic«Ki;?fo|^Hi 

 p. 440 and 523. . ...-., , ,, „, i, . 



