EXISTING GLACIERS. 11 



to its foot. The Mer de Glace, which descends from Mont 

 Blanc to the valley of Chamounix, has a length of about 

 eight miles below the we've-field. In all, there are esti- 

 mated to be twenty-four glaciers in the Alps which are 

 upwards of four miles long, and six which are upwards of 

 eight miles in length. The principal of these are the Mer 

 de Glace, of Chamounix, on Mont Blanc ; the Gorner 

 Glacier, near Zermatt, on Monte Rosa ; the lower glacier 

 of the Aa-r, in the Bernese Oberland ; and the Aletsch 

 Glacier and Glacier of the Rhone, in Vallais; and the 

 Pasterzen, in Carinthia. 



These glaciers adjust themselves to the width of the 

 valleys down which they flow, in some places being a mile 

 or more in width, and at others contracting into much 

 narrower compass. The greatest depth which Agassiz 

 was able directly to measure in the Aar Glacier was two 

 hundred and sixty metres (five hundred and twenty-eight 

 feet), but at another point the depth was estimated by 

 him to be four hundred and sixty metres (or fifteen hun- 

 dred and eighty-four feet). 



The glaciers of the Alps are mostly confined to the 

 northern side and to the higher portions of the mountain- 

 chain, none of them descending below the level of four 

 thousand feet, and all of them varying slightly in extent, 

 from year to year, according as there are changes in the 

 temperature and in the amount of snow-fall. 



The Pyrenees, also, still maintain a glacial system, but 

 it is of insignificant importance. This is partly because 

 the altitude is much less than that of the Alps, the cul- 

 minating point being scarcely more than eleven thousand 

 feet in height. Doubtless, also, it is partly due to the 

 narrowness of the range, which does not provide gathering- 

 places for the snow sufficiently extensive to produce large 

 glaciers. The snow-fall also is less upon the Pyrenees 

 than upon the Alps. As a consequence of all these con- 

 ditions, the glaciers of the Pyrenees are scarcely more 



