MONT BLANC THE ALPS AND RHONE. 87 



course peculiarly exposed to the destroying 

 powers in question. Glaciers and avalanches 

 sweep down from their sides the crumbling 

 particles, in the form of mud, pebbles, and 

 detritus, or crushed rubbish, and thus supply 

 the impetuous river A*rne, which descends from 

 these lofty regions. " Scarcely," says Sir C. 

 Lyell, " has the Rhone passed out of the Lake 

 of Geneva before its pure waters are filled with 

 sand and sediment by the Arne. The Rhone 

 afterwards receives vast contributions of trans- 

 ported matter from the Alps of Dauphigny, 

 and the volcanic mountains of central France ; 

 and when at length it enters the Mediterranean, 

 it discolours the blue waters of that sea with a 

 whitish sediment for the distance of between six 

 and seven miles." The Red River of Louisiana 

 is so full of the disintegrated particles derived 

 from a region of red porphyry rocks through 

 which it flows, as to have received its name 

 from the fact ; the river deposits its sediment 

 on its banks in regular layers of red. Many 

 other rivers are coloured blue, black, yellow, and 

 brown from similar causes. The very names of 

 the Ganges and Nile are so associated with the 

 fertilizing influence of the mud they convey, as 

 scarcely to make it necessary to allude to them 

 in illustration of this subject. But it may be 

 mentioned as affording us somewhat of an illus- 



