20 THE CLIMATIC FACTOR AS ILLUSTRATED IN ARID AMERICA. 



may show an unbroken slope, gentle or steep as the case may be, or may be broken into 

 four or five terraces. Practically every waterway, large or small, is bordered by one or 

 more terraces. They form the third of the persistent elements of the landscape. Not so 

 noticeable as the rough mountains, not furnishing a home and land for tillage to the ancient 

 inhabitants like the bahadas, they are in some ways quite as important. Their interpreta- 

 tion, unlike that of the other featvu-es, is by no means a matter of general agreement. 

 Therefore, when we have briefly discussed the vegetation of the country, I shall devote a 

 chapter to a consideration of the two opposing theories, climatic and tectonic, which have 

 been advanced in explanation of the terraces. 



