1 



Evolution of Modern Surface Features 



of Western North America' /<- ^o^s Hn^-^ 



Philip B. King ^*^jl 



United States Geological Survey, " 

 Menlo Park, California 



In preparing a summary of the geological 

 background of the origins and affinities of the land and fresh- 

 water faunas of western North America, I am faced with several 

 difficulties. 



First is the well-known lack of communication between the 

 sciences — a difference in language, in thinking, and in emphasis. 

 Thus, items that may be decisive to a zoologist may receive little 

 attention from a geologist. I welcome this opportunity to bridge a 

 gap between the zoological and geological sciences, to make a con- 

 tribution to a problem shared by both of us, and to enhance my own 

 education. At the same time, I must admit my present ignorance of 

 facets of the problem which are not geological, so that my analysis 

 in this paper must be mainly geological. 



Then, too, even in making a purely geological analysis of the 

 problem one discovers wide gaps in the record, much evidence that is 

 equivocal rather than decisive, and much divergence among geolo- 

 gists as to what the evidence means. Broadly, the subject here 

 treated is the evolution through time of the geological features of 

 western North America, but the aspect of most zoological interest is 

 evolution of the surface forms only. For the record up to the middle 

 Tertiary, the surface forms must be deduced from rocks and struc- 

 tures of various ages, since none of the landscape of that time is 

 now preserved. Some fragments of surface forms as old as middle 

 Tertiary are preserved, and younger ones are preserved in in- 



1 Publication authorized by the Director, United States Geological Survey. 



3 



