1916] Weaver: Tertiary Faunal Horizons 3 



EOCENE 



Igneous and sedimentary deposits of Eocene age occur in the western foot- 

 hills of the Cascade Mountains, in southwestern Washington, in portions of the 

 Puget Sound Basin and around the margins of the Olympic Peninsula. The sedi- 

 mentary deposits within the western Cascade Mountains are almost entirely of 

 fluviatile and estuarine origin. Those in southwestern Washington are predomi- 

 natingly marine. The intervening area extending from Puget Sound to the vi- 

 cinity of Portland, Oregon, contains alternating deposits of marine and brackish 

 water origin together with bands of fresh water shales. Basalts and basaltic 

 tufts are commonly intercalated with all these phases. 



In King and Pierce counties Eocene sedimentary formations attain a thick- 

 ness of at least ten thousand feet. They consist of non-marine sandstones, shales 

 and conglomerates together with carbonaceous shales and coal seams which have 

 been more or less intensely folded. Fossil plant remains occur within these de- 

 posits but no marine molluscan remains are known. A few brackish water fossils 

 have been found, several species of which occur associated with the marine and 

 brackish waters faunas in southwestern Washington. Strata containing marine 

 fossils occur between South Seattle and Renton and are characteristic of the 

 upper Eocene or Tejon of California. These strata are directly interbedded with 

 the estuarine deposits occurring to the eastward near Coal Creek and Franklin. 

 Upon the evidence afforded by the occurrence of fossil bearing marine Tejo strata 

 interbedded with the purely estuarine phase as well as the presence of typical 

 Eocene fossil floras, the brackish water deposits of the western foothills of the 

 Cascade Mountains are correlated with the typically marine Eocene deposits of 

 southwestern Washington. 



The most complete section of the Eocene in western Washington occurs in 

 southern Lewis County along Olequah Creek and Cowlitz River. The lower por- 

 tion of this section, as exposed along Stillwater Creek to the southwest of Vader 

 and as far south as Olequah, is of marine origin. Stratigraphically above the base 

 these strata grade into those of brackish water origin and finally into those con- 

 taining a fresh water fauna. Still higher in the section they revert back to a 

 brackish water condition and finally to a marine. They continue as marine de- 

 posits to the top of the section. The total thickness of the section as measured 

 from Olequah to Winlock is approximately 4,000 feet. Stratigraphically below 

 the base of this measured section there are approximately 6,000 feet of sediments 

 and intercalated basalts. 



The marine faunas occurring within the measured section are typically upper 

 Eocene and are very similar to the Tejon of California. The uppermost beds as 

 exposed about one and one half miles east of the town of Vader on Cowlitz River 

 at fossil localy No. (1) are possibly the equivalent of the Rimella simplex 1 Zone 

 of the Tejon of California. The strata exposed between Vader and Olequah are 



iDickerson, R. E. Note on the Faunal Zones of the Tejon Group, TJniv. Calif. Publ. 

 Bull. Dept. Geol., Vol. 8. pp. 17-25. 1914. 



