GREAT EROSION AL WORK OF WINDS Ail 



perplexing phenomena concerning the larger features of earth than any 

 one of the great themes mentioned and perhaps more than all of them 

 combined. It projects the imagination backward to the beginnings of 

 geologic history; and it carries it forward to the end of time. In the 

 lineaments of our dead moon it may be we behold the final effect of 

 eolic powers. 



Although perhaps not wholly the unaided work of any one man or 

 group of men, the generalization of regional eolation is first distinct- 

 ively American in origin. As such it seems not too much to say that 

 it is allotted to stand as one of the far-reaching achievements of our 

 century. It is doubtless the last of the great discoveries in geologic 

 science to be attained by purely observational methods. The future 

 advancements in earth-study must be quantitative instead of qualitative 

 in character. They must be the direct outcome of mathematical inves- 

 tigation, of the rigid application of the new physico-chemical laws, and 

 of the complete evolution which the discovery of radio-activity has 

 imposed. 



This, then, is briefly a statement of the theory of regional eolation. 



