F^ ' :^«-j«-^ 



THE TRACK OF A GLACIER. 



LIFE HISTORY OF A MOUNTAIN— II 



By J. LOMAS, F.G.S., A.R.C.S. 



WE have already passed in review 

 some of the principal agents 

 whose function it is to break up 

 rock masses. 



We saw that frost and sun flake off 

 fragments which fall and accumulate 

 near the place where the disintegration 

 takes place. It is evident that if this 

 action continued for a considerable time 

 the rock would become covered with its 

 own waste and would be preserved from 

 further decay. 



In places remote from agents of 

 transport this actually happens, but if 

 the dihris comes within the influence of 

 moving water, ice or air, the fragmental 



material is carried away and the rocks 

 are left exposed to fresh attacks. 



Within broad limits we can say that 

 each tool leaves its own characteristic 

 mark on the rock which it is abrading. 



In its action the sea may be compared 

 with a horizontal saw ; it undercuts the 

 cliff against which it works, and removes 

 the dibris as it falls from above. A river 

 cuts like a vertical saw. A country which 

 has been covered by a glacier api^ears as 

 though it had been gouged and sand- 

 papered in one direction, and scratches 

 are left on the polished rocks showing the 

 same trend as the direction of ice move- 

 ment. 



332 



