DEPOSITIONAL PHASES OF EOLATION UNDER THE STIMU- 

 LUS OF ARIDITY. 



BY CHARLES R. KEYES. 



(Abstract.) 



It is now a question whether wind-scour under the stimulus of a typi- 

 cally arid climate is not actually the most potent and persistent of the 

 erosive agencies. Under favorable conditions its general efficiency must 

 greatly exceed that of stream-action in normally moist lands. At any 

 rate, erosionally, its world's work is probably surpassed neither by that 

 of hydrasion nor of glaciation. 



Notwithstanding the fact that the eolative processes are as sharply 

 defined in their operations as are the several phases of either of the other 

 two great erosive agencies it is mainly only some of the minor trans- 

 portative features which usually attract attention. Even in regions of 

 their maximum efficiency, and where often they are almost the sole 

 erosive agent, their most striking results are frequently mistaken for 

 mere idle shifting of desert sands'. The most recent observations in desert 

 and Kemi-arid regions strongly emphasize the great importance and vast- 

 ness of the depositional products of eolation. 



Under various titles are the different phases of erosional processes 

 considered. The majority of the terms are rather loosely applied and 

 usually refer to complex phenomena rather than to a single simple activ- 

 ity. For present purposes these terms appear to be best restricted to 

 tlie following scheme : 



GENERAL. WATER WIND ICE 



Erosion Hydrasion Eolation Glaciation 



Weathering Decomposition ....Insolation Refrigeration 



Transportation . . . Flotation Deflation Crystportation 



Deposition Sedimentation Aeroposition Morainization 



For the general geologic work of the winds W. J. McGee's term eola- 

 tion appears to be the happiest expression. 



Under climatic conditions of aridity the phenomenon of rock-weather- 

 ing is influenced so little by the action of chemical decay that the prod- 



