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



portion of the Tejon epoch but had almost entirely ceased by 

 the opening of the Oligocene epoch. Near the close of the 

 Eocene or at the opening of the Oligocene minor crustal move- 

 ments brought about an encroachment of the marine waters 

 into the Piiget Sound basin and also into the present site of the 

 Strait of Juan de Fuca. 



In southwestern Washington the oldest deposits of post- 

 Eocene age occur west of the city of Centralia in the valley 

 of Chehalis River. They consist of indistinctly bedded, sandy, 

 gray shales containing a marine invertebrate fauna which will 

 be referred to in this report as the Molopophorus lincolnensis 

 zone. The strata containing the fauna may be referred to as 

 the Lincoln horizon. At the present time the strata at this 

 locality are approximately 1,000 feet in thickness. Away from 

 stream, railway or wagon road cuts, rock exposures are largely 

 obscured by a veneer of sands, clays and gravels, rendering it 

 difficult to determine the exact areal limits of these beds. 

 Fossiliferous strata outcropping in the banks of Olequah Creek 

 near the town of Winlock and in the banks of Cowlitz River, 

 six miles east of Vader, at the Graeco Ranch, may have been 

 contemporaneously deposited with those at Lincoln Creek. 

 The same may be true of the shales on Porter Creek north of 

 the town of Porter in Chehalis County. They are unknown 

 to the southwest in Pacific and Wahkiakum counties, as well 

 as along the Strait of Juan de Fuca. 



Toward the close of deposition of the Lincoln sediments 

 the Oligocene seas expanded and occupied portions of the 

 Strait of Juan de Fuca and the Puget Sound basin, as well as 

 most of southwestern Washington. By the close of the Oli- 

 gocene epoch these deposits had attained a maximum aggre- 

 gate thickness of 15,000 feet. They consist predominately of 

 shales and sandy shales within which local beds of conglom- 

 erate and sandstone are occasionally interbedded. The thick- 

 est and most complete section of the Oligocene is to be found 

 in northern Clallam County along the northern border of the 

 Olympic Peninsula. The section measured between Cape Flat- 

 tery and Clallam Bay possesses a thickness of 13,300 feet. The 

 basal beds are situated at the west end of Wyatch Slough and 

 the upper about half way between Neah Bay and Clallam Bay. 



