20 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Ser. 



scured by clays, sands and gravels of fliiviatile origin. In many 

 areas the Tertiary rocks themselves have been so deeply weath- 

 ered that very little information can be obtained concerning 

 their lithologic character and structure. All parts of western 

 Washington are clothed with a dense growth of forest and 

 underbrush, which conceals many exposures of Tertiary rocks 

 which are not covered with Pleistocene sands and gravels. 



LITERATURE 



Numerous references to the occurrence of Tertiary strata 

 may be found in papers dealing with the geology of western 

 Washington. The majority of these papers mvoive investiga- 

 tions of economic products such as coal and contribute little to 

 the purely scientific phases of Tertiary geology. Only the more 

 important literature is here reviewed. 



James D. Dana referred to Tertiary strata in the report 

 on the geology of the United States Exploring Expedition 

 under Wilkes^ as occurring to the north of Columbia River 

 and along the shores of Puget Sound and the Strait of Juan 

 de Fuca. Collections were made from the south side of 

 Columbia River at the town of Astoria. This fauna was iden- 

 tified by Conrad, who regarded it as Miocene. 



Marine Neocene deposits are mentioned by Dr. Bailey 

 Willis as occurring near Seattle immediately north of the 

 northern limits of the Tacoma quadrangle.^ These deposits 

 are not described. 



The first detailed description of the occurrence of Oligo- 

 cene-Miocene strata within the state is to be found in a report 

 by Dr. Ralph Arnold^ on a "Geological Reconnaissance of the 

 Coast of the Olympic Peninsula, Washington." Oligocene- 

 Miocene deposits are described as occurring along the north- 

 ern border of the Olympic Peninsula. Pliocene deposits are 

 mentioned as being present on the west coast of the peninsula 

 near the mouth of Oueniult River. The Miocene deposits are 

 composed of conglomerates, sandstones and shales which at- 



'Dana, J. D., in U. S. Exploring Expedition, under command of Charles Wilkes, 

 U. S. N., Philadelphia, vol. 10. 1838-1842. 



"Willis, Bailey, Tacoma Folio, No. 54, U. S. Geological Survey, 1896. 



'Arnold, Ralph, Bulletin Geological Society of America, vol. 17, pp. 451-468, 

 September, 1906. 



