TERTIARY FAUNAS OF THE PACIFIC COAST 229 



alternated. It is obvious, therefore, that the legends on the maps are 

 very general. Only in those instances where the body of water 

 indicated as fresh remained fresh throughout practically the whole 

 of its existence is it indicated as a freshwater area on the map. 



The periods chosen for representation and as units for discussion 

 are neither of equal length nor of equal importance, and the lines 

 separating them are in some instances arbitrary; but it is believed 

 that they serve the purpose of systematizing the discussion better than 

 any other plan of subdivision. The data are incomplete and the 

 conclusions admittedly tentative, and it is expected that future 

 investigations will disclose new and important information, which 

 will necessitate alterations, but the fact remains that general reports 

 of this kind, based as they are on the present state of our knowledge, 

 often point the way to more exact results in the future. 



ACKNOWLEDGMENTS 



The writer wishes to acknowledge his indebtedness to Messrs. 

 Bailey Willis, J. S. Diller, T. W. Stanton, Robert Anderson, Chester 

 W. Washburne, and several others for personal assistance in the 

 preparation of the text and maps, and to express his thanks for the 

 services rendered. In addition to the personal aid received, the 

 literature relating to the subject of West Coast geology has been 

 freely drawn on in the compilation of relevant data and in many cases 

 proper acknowledgment for this is made in the text. 



THE EOCENE PERIOD 

 RELATION OF THE EOCENE TO THE CRETACEOUS 



Before entering into the details of the geologic history of the 

 Tertiary it is well to consider for a moment the relations existing 

 between the earliest Tertiary rocks and those of the Cretaceous, and 

 to note the conditions initiating the Tertiary, as implied by these 

 relations. 



A widespread unconformity exists between the Eocene and the 

 Cretaceous on the Pacific Coast of North America. Throughout 

 Washington, Oregon, and certain parts of California, this uncon- 

 formity is angular, while over considerable areas in California and 

 at one locality in Oregon the unconformity may only be recognized 

 by a more or less marked hiatus in the faunas. 



