400 



University of California Publications in Geology [Vol. 8 



FAUNA 



The San Pablo Bay section is here separated for the purposes of 

 this paper into two parts, A and B. These divisions are in reality 

 famial divisions. As will be shown later, two major fannal zones are 

 recognizable in the San Pablo of Middle California. The divisions 

 A and B, as used here, are the stratigraphic equivalents of these zones. 

 Division A of the type section includes the lower members of the group, 

 from the base to the irregular contact described above and possibly 

 somewhat higher. This part of the section is about nine hundred feet 

 thick. Division B includes the upper members of the group above the 

 irregular contact, the thickness of which is about thirteen hundred 

 feet. 



Division A. — Three minor faunal zones are recognizable in division 

 A. The lower two of these zones are based upon the sea-urchins therein 

 contained. At the bottom of the series, the species Scutella gabbii is 

 found abundantly; two hundred feet stratigaphically above, Scutella 

 gabbii is but rarely found and Astrodapsis tumidus subsp. cierboensis 

 makes its appearance. At the time Dr. Merriam 20 wrote his paper 

 outlining the faunal zones of the San Pablo on the basis of the sea- 

 urchins, it was believed that the Scutella gabbii and Astrodapsis 

 tumidus zones did not overlap. Later work has shown that the species 

 Scutella gabbii extends into the upper Astrodapsis beds. 



At this point in the discussion, it may be well to call attention to 

 the fact that with Astrodapsis tumidus subsp. cierboensis in the second 

 minor faunal zone of division A, is found Scutella pabloensis Kew, 

 both of which are found on the south side of the Mount Diablo anti- 

 cline at a horizon believed to be the same as that in which they are 

 found on San Pablo Bay. 



The third minor faunal zone is one that has not been recognized 

 outside of the bay section. The fauna of this zone comes from the 

 tine sandstones at the top of division A where several species that do 

 not appear in the coarser sandstones below have been found. These 

 are Dosinia merriami, Pitaria behri, Pitaria stalderi, Calliostoma sp. 

 indt. and Ficus cf. stanfordensis. Of these, the last four species have 

 not been found outside of this section. 



The species which appear to be characteristic of division A and of 

 the lower San Pablo throughout middle ■ California are Astrodapsis 

 tumidus subsp. cierboensis, Scutella pabloensis, Pecten weaveri, 



20 Merriam, J. C, The Distribution of the Neocene sea-urchins of Middle 

 California, Univ. Calif. Publ. Bull. Dept. Geo!., vol. 2, no. 4, pp. 109-118, 1898. 



