Oh. XVI.] 



TEANSPORTATION OF ROCKS BY GLACIERS. 



375 



* 



they afterwards move on together, in the centre, if the 

 confluent glaciers are equal in size, or nearer to one side if 



unequal. 



Fragments of stone and sand, which fall through crevasses 

 in the ice and get interposed between the moving glacier and 

 the fundamental rock, are pushed along so as to have their 

 angles more or less worn off, and many of them are entirely 

 oTonnd down into mud. Some blocks are pushed along be- 

 tween the ice and the steep boundary rocks of the valley, and 

 these, like the rocky channel at the bottom of the valley, often 

 become smoothed and polished, and scored with parallel fur 



r 



minerals 



such as crystals of quartz, which act like the diamond upon 

 glass.* This effect is perfectly different from that caused by 

 the action of water, or a muddy torrent forcing along heavy 

 stones ; for these not being held fast like fragments of rock in 

 ice, and not being pushed along under great pressure, cannot 

 scoop out long rectilinear furrows or grooves parallel to each 

 other. f The discovery of such markings at various heights 

 far above the surface of the existing glaciers and for miles 

 beyond their present terminations, affords geological evidence 

 of the former extension of the ice beyond its present limits 

 in Switzerland and other countries. 



The moraine of the glacier, observes Charpentier, is en- 

 tirely devoid of stratification, for there has been no sorting 

 of the materials, as in the case of sand, mud, and pebbles, 

 when deposited by running water. The ice transports indif- 

 ferently, and to the same spots, the heaviest blocks and the 

 finest particles, mingling all together, and leaving them in 

 one confused and promiscuous heap wherever it melts. J 



In the foreground of the woodcut, fig. 22, page 368, some 

 dome-shaped masses of smoothed rock are represented, called 

 in Switzerland ' roches moutonnees/ for they are compared 

 to the backs of sheep which are lying down. These owe their 



* 



rounded and smooth outline to the action of the glacier 

 when it was more in advance, and the inequalities of the hard 



* See Elements of Geol. ch. xi. 

 t Agassiz, Jam. Ed. New Phil. Journ. 

 No. 54, p. 388. 



$ Charpentier, Ann. des Mines, torn, 

 viii. ; see also Papers by MM. Venetz 

 and Agassiz. 



