CHAPTER X. 



ICE AND ITS WORK. 



Although our attention was restricted in the last chapter 

 to the action of rain and rivers, it would be a great mistake 

 to suppose that these are the only agents by which denu- 

 dation is effected. Rain and rivers unquestionably do much 

 in the way of destruction, but they work with far greater 

 effect when aided by the action of frost. Bare faces of 

 hard rock may be exposed to the action of rain, year after 

 year, without suffering any marked change : the water may 

 fill the pores and fissures of the rock ; yet, unless the mineral 

 components happen to be easily decomposed, it will eat 

 its way into the stone with extreme slowness. But when a 

 frost comes on, the conditions are entirely changed, and a 

 fresh element of destruction is introduced. The water 

 with which the rock is charged freezes into ice and, during 

 its solidification, it tends to expand, as explained in a 

 previous chapter. If the water be confined in the pores 

 and cracks of the rock, the tendency is resisted ; but the 

 particles, in freezing, push each other apart in all directions, 

 with such force, that the strongest rock is sooner or later com- 

 pelled to yield. Just as a water-pipe bursts during a frost, 

 so the rock ultimately gives way. Fragments of stone, often 



