38 



THE DESERT 



of heavy bowlders are piled on either side of 

 mountain water-courses, looking as though ice 

 may have caused their peculiar placing. But 

 there is no certainty about any of these. Land 

 slips may have made the windrows as easily as 

 ice slips ; and water can heap mounds of sand 

 and gravel as readily as glaciers. One cannot 

 trace the geological ages with such facility. 

 Things sometimes "just happen/' in spite of 

 scientific theories. 



Besides, the movement of the stones into the 

 valleys is going on continuously, irrespective of 

 glaciers. They are first broken from the peaks 

 by erosion, and then they fall into what is called 

 a talus a great slope of stone blocks beginning 

 half way down the mountain and often reaching 

 to the base or foot. Many of them, of course, 

 are rolled over steep declivities into the canyons 

 and thence carried down by flood waters ; but 

 the talus is the more uniform method for bowl- 

 ders reaching the plain. 



In the first stage of the talus the blocks are 

 ragged-edged and as large as a barrel. Nothing 

 whatever grows upon the slope. It is as bare as 

 the side of a volcanic crater. And just as diffi- 

 cult to walk over. The talus is added to at the 

 top by the falling rock of the face-wall, and it 



