SCULPTURING EFFECTS OF GLACIERS. 



149 



ward on its bed, where it ploughs up the stones, breaks up the rocks, 

 and, adding their spoils to the accumulations from avalanches, rinally 

 throws down huge banks of rubbish at the foot of the glacier, which 

 is thus surrounded by an immense mass of loose materials, called the 

 terminal moraine, which is deposited as the ice melts. 



Almost every valley in the Alps is more or less filled with this 

 morainic matter, a mixture of angular stones and mud, which is often 

 cut into by small streams. Every river bed in the dry season is a floor 

 of large stones, more or less rounded, which travelled on the glacier 



Fig. 47. Track of a Glacier, Mer de Glace, showing median moraines. 



before they were driven along by the mountain torrent and worn. 

 The glacier wears its bed smooth, partly by the abrading action of 

 rock fragments, which fall through cracks produced when the ice- 

 stream squeezes through a defile, when they become unbedded in its 

 floor, and rasp, groove, and scratch the subjacent rocks as the ice 

 moves onward and grinds them into mud. Rocks thus worn show that 

 succession of small rounded bosses which, from their resemblance to 

 the backs of a flock of sheep, have been named rovhes moutonnees ; 

 they are well seen in Cwm Arthur, near Ffestiniog. The striated 



