562f C. R. KEYES THE GEOGRAPHIC CYCLE IN AN ARID CLIMATE 



plains surface, and this is constantly lowering. This feature is especially 

 well shown in the Caballos and Plomas ranges (figures 1 and 2). On 

 the basis of water action alone, the most inexplicable feature of desert 

 configuration has always been how around the periphery of a mountain 

 block a broad, perfect plain is produced, while in the middle a lofty, 

 rugged mountain ridge exists. In the light of the changed angle at 

 which the facial expression of the desert ranges is viewed, the alleged evi- 

 dences of energetic storm work have to be critically examined anew. 

 Bearing directly upon this point, it is not without great interest to note an 

 expression of opinion by the late S. F. Emmons, than whom no one was 

 probably more familiar with the arid regions of the West during a period 

 covering more than 40 3^ears. In the spring of 1903, when he was pay- 

 ing me a fortnight's visit at Socorro, he remarked that he was completely 

 nonplussed that the desert mountain ranges should present such youthful 

 topograph}^ on so huge a scale, and yet display so little evidence of ade- 

 quate means with which to accomplish it ; and he further stated, concern- 

 ing the unsatisfactory character of all existing explanations, that in all 

 his long experiences in the West this feature was the most puzzling of 

 any which he had encountered or which had ever confronted geologists. 

 At that time I had already followed the aqueous development of the relief 

 features of the region to its necessary and wholly inadequate conclu- 

 sions, and I had already begun to grasp the fundamental significance 

 of the rock-floors of the arid intermont plains and the tremendous effi- 

 ciency of wind-scour upon dry rock surfaces. Near the conclusion of the 

 long discussions which this view aroused, Mr. Emmons dropped the state- 

 ment that the conception was too new for him to grasp all at once, but 

 that he believed that there was great merit in the wind explanation. It 

 was, however, a full lenstrum before he told me one day that he had come 

 to believe that the only, adequate solution of the vexed problem would be 

 through means of the wind and not water. 



Eecapitulation 



The larger geographic features of deserts appear to find no adequate 

 explanation of their origin hj any known method of stream corrasion. 

 For them wind-scour alone satisfactorily accounts. The necessary con- 

 sequences of a strictly deflative hypothesis for the genesis of desert land- 

 scapes is everywhere amply supported by recently recorded observations. 

 The geographic cycle in an arid climate is logically developed by consid- 

 ering wind action and not water action as the prime erosional process. 

 For topographic detail important water action of normal character is not 

 precluded. 



