152 LIGHT SCIENCE FOR LEISURE HOURS. 



A country like Switzerland must always be liable 

 to the occurrence, from time to time, of catastrophes 

 of this sort. Or rather, perhaps, we should draw a 

 distinction between the two divisions of Switzerland 

 referred to above. Of these the one may be termed 

 the mountain half, and the other the lake half of the 

 country. It is the former portion of the country 

 which is principally subject to the dynamical action 

 of water. A long-continued and heavy rainfall over 

 the higher lands cannot fail to produce a variety of 

 remarkable effects, where the arrangement of moun- 

 tains and passes, hills, valleys, and ravines, is so com- 

 plicated. There are places where a large volume of 

 water can accumulate until the barriers which have 

 opposed its passage to the plains burst under its in- 

 creasing weight ; and then follow those destructive 

 rushes of water which sweep away whole villages at 

 once. It is, in fact, the capacity of the Swiss moun- 

 tain-region for damming up water, far more than any 

 other circumstance, which renders the Swiss floods so 

 destructive. 



And then it must be remembered that there are at 

 all times suspended over the plains and valleys which 

 lie beneath the Alpine ranges enormous masses of 

 water in the form of snow and ice. Although in gen- 

 eral these suffer no changes but those due to the par- 

 tial melting which takes place in summer, and the re- 

 newed accumulation which takes place in winter, yet 



