NATIONAL ACADKMY BIOGRAPHICAL MEMOIRS VOL. VIII 



that a physiographic turn was given to Powell's work, not so 

 much from his own intentional preference or selection, but 

 from the abundant and open opportunity for physiographic 

 study in a semi-arid region, for, in common with nearly all 

 the early geological explorers of the West, Powell was led by 

 his environment to give much attention to surface forms ; he 

 could not fail to see their intimate relation to internal struc- 

 ture, so wonderfully displayed by reason of the scantiness or 

 absence of vegetation. He therefore inevitably described the 

 relief of his region by explaining it, and his explanation was 

 presented in terms of structural masses, raised by internal 

 diastrophic forces and worked upon by external destructive 

 forces. k He emphasized internal or "geological" structure as the 

 prime basis for the classification of land forms, and adopted as 

 the guide to their secondary grouping the erosion of what he 

 called "concomitant," or, as would now be said, sequential, 

 minor forms. \ He did not explicitly make the next step cf 

 systematically~o!escribing the stages in the progress of erosion 

 during its work upon uplifted masses, but it must be a careless 

 reader who does not repeatedly find this principle implied in a 

 careful study of Powell's writings. At this time, as well as 

 later, Powell had the great advantage of discussing his prob- 

 lems with a younger investigator of the Cordilleran region, 

 whose sound views probably had a larger influence in shaping 

 his senior's opinions than will ever be directly known. 



As to the action of erosional processes, Powell's reports 

 abound in quotable statements, of which the following are 

 good examples : "Erosion is not greatly promoted by increased 

 rainfall. . . . With greater rainfall we have greater 

 power, but a lesser utilization of the power; with lesser rain- 

 fall we have lesser power, but greater utilization ; and in these 

 varying conditions, just where maximum degradation is found 

 I am not able to state." "I have many times witnessed the 

 action of a storm in an arid region where the disintegrated 

 rocks were unprotected by forests, shrubbery, or turf, and as 

 often have T been impressed with the wonderful power of the 

 infrequent storm to gather up and carry away the land, as 

 compared with the frequent storm in the prairie or forest of a 

 land more richly clad" (Uinta, 188; see also Colorado River, 



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