Vol. VI] WEAVER— EOCENE OF LOWER COWLITZ VALLEY \y 



Pacific Railway line from Centralia to Portland. An interpre- 

 tation of the stratigraphic section shows that this shore line 

 was alternately shifting east and west as the sea floor was be- 

 ing differentially elevated and depressed. The effect of those 

 diastrophic movements as recorded within the area involved in 

 this paper may be seen in the passage from marine to brackish 

 and fresh water and thence back again to marine. The marine 

 faunas as listed above indicate tropical climatic conditions and 

 an environment ranging from shallow water to moderately 

 deep water. 



CONCLUSIONS 



Within the area studied between Winlock and Olequah 

 there are about 4000 feet of shales and shaly sandstones of 

 upper Eocene age. Beneath these, between Olequah and Castle 

 Rock, there are possibly 6000 feet of unmeasured upper Eocene 

 sandstones and shales, together with numerous intercalated 

 layers of basaltic lavas. Overlying the Eocene in the vicinity 

 of Winlock and at the Graeco ranch on Cowlitz River are 

 marine deposits of Oligocene age. A section of the Eocene 

 measured between Olequah and Winlock consists of a lower 

 division of marine beds at least 400 feet in thickness. This is 

 overlaid by 550 feet of brackish water strata and that in turn 

 with 300 feet of freshwater beds. Above the freshwater beds 

 are 520 feet of brackish water strata. Above these are marine 

 beds having a thickness of 2410 feet. These strata are all fos- 

 siliferous and appear to be most closely related to the middle 

 Tejon as described in the Mount Diablo region of central 

 California. 



The basement upon which the Tejon in this area rests, as 

 in the case of most of w-estern Washington, is unknown. The 

 fauna of the upper portion of the Cowlitz section bears a close 

 relation to the overlying Molopophorus lincolnensis zone of 

 the lower Oligocene as represented to the north in the vicinity 

 of Lincoln Creek, in Thurston County. 



