24 



THE DESERT 



Plains, val- 

 leys, and 

 mesas. 



Effect of 

 drought. 



are always circling yon with a ragged horizon, 

 dark-hned, bare-faced, barren just as truly 

 desert as the sands which were washed down 

 from them. Between the ranges there are 

 wide-expanding plains or valleys. The most 

 arid portions of the desert lie in the basins of 

 these great valleys flat spaces that were once 

 the beds of lakes, but are now dried out and 

 left perhaps with an alkaline deposit that pre- 

 vents vegetation. Through these valleys run 

 arroyos or dry stream- beds shallow channels 

 where gravel and rocks are rolled during cloud- 

 bursts and where sands drift with every wind. 

 At times the valleys are more diversified, that is, 

 broken by benches of land called mesas, dotted 

 with small groups of hills called lomas, crossed 

 by long stratified faces of rock called escarp- 

 ments. 



With these large features of landscape com- 

 mon to all countries, how does the desert differ 

 from any other land ? Only in the matter of 

 water the lack of it. If Southern France 

 should receive no more than two inches of rain 

 a year for twenty years it would, at the end of 

 that time, look very like the Sahara, and the 

 flashing Rhone would resemble the sluggish 

 yellow Nile. If the Adirondack region in New 



