1915] 



Clark: Fauna of the San Pablo Group 



391 



That part denoted as Pliocene by Turner includes what is now recog- 

 nized as the San Pablo Group, the Pinole Tuff and the Orindan. 



Turner gave a list of sixteen species of marine invertebrates, which 

 was evidently taken from Gabb's paper; he also listed five others 

 determined by Dall. These came from the north side of Mount Diablo 

 in the vicinity of Kirker Pass. 



In the paper just referred to, Turner also gave three lists of fossil 

 leaves collected from strata now recognized as belonging to the San 

 Pablo Group. One collection is from the north side of Mount Diablo 

 and the other two are from the south side. Lesquereux, who deter- 

 mined the plant species, referred those from the north side of the 

 mountain to the Pliocene and those from the south side to the Miocene. 



The first writer to apply the name "San Pablo" and to differentiate 

 it definitely from the formations above and below, was Professor J. C. 

 Merriam, 5 in a paper entitled "The Distribution of the Neocene Sea- 

 Urchins of Middle California," The purpose of this paper was to 

 indicate the faunal zones of the Neocene, using the sea-urchins as the 

 most characteristic species. In referring to the San Pablo, Merriam 

 says : 



The series of strata characterized by the presence of Astrodapsis and Scutella 

 (Clypeaster) gabbi may, with reference to its most important features, be treated 

 as a distinct formation and will be referred to in this paper as the San Pablo 

 Formation. 



The sea-urchins form the most prominent organic feature of the formation, 

 neither of the Astrodapsis species being found outside of it. The zone of 

 Scutella gabbi is not always present, but may be considered as belonging to the 

 formation. 



Merriam concluded that the San Pablo was an older formation 

 than the Merced, the type section of which is situated just across 

 the bay to the southwest of the type section of the San Pablo. He 

 says : 



If the Merced series be Pliocene, the San Pablo must be below the Upper 

 Pliocene at least. It has already been shown to rest above what has been 

 considered Miocene in Contra Costa County. In other words, it probably repre- 

 sents Middle Neocene. Such a determination of the age of this formation, it 

 will be noticed, was, to some extent, foreshadowed by the reference of different 

 localities of the same beds indifferently to the Miocene or Pliocene by the 

 earlier writers on the geology of this region. 



Two faunal zones were outlined in the San Pablo by Merriam ; 

 one was called the Scutella gabbi zone, the other the Astrodapsis zone. 



s Univ. Calif. Publ. Bull. Dept. Geol., vol. 2, no. 4, pp. 109-118, 1898. 



