1918] 



I 'an Winkle: Paleontology of the Oligocene 



77 



OLIGOCENE FAUNA [Continued] 



CONDITIONS OF ENVIRONMENT 



The faunas occurring in the lower Porter beds as exposed above the Eocene 

 contact on Porter Creek in the conglomerate west of Oakville are typically littoral 

 species, as represented by the Acmaeidae, Ostreidae, Mytilidae, etc. The waters 

 in which these fauna lived were tropical, as indicated by the presence of the genus 

 Cypraea and corals. The marine molluscan fauna found in the vicinity of the Greece 

 ranch, at the south end of the Oligocene Chehalis embayment, appears to have lived 

 in water ranging in depth from possibly two to twenty fathoms. The conglomeratic 

 character of the rock as well as the presence of such shallow water genera as 

 Patella and Littorina indicate a near-shore fauna, but the association with these of 

 such genera as Rissoa, Leda, Lima and Strepsidura point to a depth of water of at 

 least twenty fathoms. The faunal assemblage as a whole may be regarded as 

 typically subtropical. 



The faunas occurring at Winlock, Lincoln Creek and the middle portion of 

 the strata exposed on Porter Creek are typically those types which live in mod- 

 erately deep water and are represented by genera which are decidedly subtropical 

 to tropical. In the upper portion of the Porter section several genera appear 

 which indicate a more temperate climate during the later portion of middle 

 Oligocene time. Such forms as Phacoides acutilineatus, Thyasira bisecta, Thracia 

 irapezmdea, are among the most common species found in the upper Oligocene or 

 Acila gettysburgensis Zone of the Puget Sound area. It is quite probable that the 

 uppermost Porter beds were being deposited contemporaneously with the lowermost 

 beds exposed in the Puget Sound embayment. 



