238 



NATURE FOR ITS OWN SAKE 



*Suruet 

 valleys. 



Valley 

 formation. 



Age of the 

 valley. 



puts on her most gorgeous garments. Occa- 

 sionally, in what are called the "sunset" val- 

 leys that is, valleys running east and west 

 there is some warmth of color, and in autumn, 

 with the yellow foliage and the Indian-summer 

 haze, there is often great display ; but during 

 the hot months the predominant note is green, 

 save where in the distant gulches and coolees 

 the blues and purples assert themselves. 



There are two ways by which the mountain- 

 valley may come into existence. The first is 

 by the cutting-away process of torrents ; the 

 second is by depression. Oftentimes the heave 

 of the fold that has lifted the mountain-peak 

 skyward has allowed the valley to sink back 

 and downward. A depression is thus formed 

 which the wear of water immediately increases. 

 Some valleys are even sunk lower than the sur- 

 rounding country so low as to make a hollow 

 and in time the waters flowing into them 

 form the long, twisting mountain-lake of 

 which the Lake of Lucerne in Switzerland is 

 an illustration. More often, however, the val- 

 ley is elevated above its surrounding plains, 

 From its walls one can always gain an approxi- 

 mate idea of its age, as from the peaks one 

 knows the age of the mountains. Abrupt sides 



