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CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Ser. 



in diameter are embedded in the clayey sandstone matrix. In 

 the stream canyons east of Waugh School many excellent 

 sections of this formation may be seen. The great abundance 

 of petrified wood which is found in the sandstones of this 

 formation is very noteworthy. In one place this material 

 formed a stratum from 8 inches to a foot in thickness. 



Two interesting faunas occur in the Petaluma formation: 

 the one, a brackish water and the other, a freshwater fauna. 

 The estuarine facies was recognized on upper Lichau Creek 

 where Corbicula calif omica (Gabb) was collected and at Cali- 

 fornia Academy of Sciences Locality No. 415. About 2.1 

 miles N. 26° E. from Elmore School in canyon and two- 

 fifths mile southeast of Mountain School road, clay shale and 

 soft, fossiliferous sandstone are found interbedded. The 

 overlying igneous rock near the contact is basalt and agglo- 

 merate. 



The best preserved specimens occur at California Academy 

 of Sciences Locality No. 415, but only two species, Corbicula 

 calif omica (Gabb) and Bittium rodcoensis (Clark), were 

 found here. These two forms, however, are also found as- 

 sociated in the uppermost portion of the San Pablo forma- 

 tion, in the Pinole syncline, on the shores of Carquinez Strait 

 and San Pablo Bay, showing that the identity of these two 

 horizons is highly probable. In other words, the Petaluma 

 formation is a freshwater and brackish water phase of the 

 marine San Pablo formation of upper Miocene age. The 

 stratigraphic relations also reinforce this correlation as both 

 the San Pablo and the Petaluma formations are unconform- 

 ably below the Sonoma group and its equivalent, the Pinole 

 tuff. Probably stratigraphically above this horizon containing 

 the brackish-water fauna is another set of beds whose clays 

 have yielded a very finely preserved collection of freshwater 

 shells. California Academy of Sciences Locality 417, where 

 these shells were obtained, is in Haggin Creek, about 200 feet 

 below the bridge on clay beds which are overlain by con- 

 glomerate one mile southeast of Penn Grove, Santa Rosa 

 Quadrangle. The strata dip 12° S. W. and have a strike of 



