Vol. 5] 



Weaver. — San Pablo Formation. 



245 



State Geological Survey, Gabb 3 mentions the presence of Scutella 

 (Clypeaster) gabbi at San Pablo Bay, Walnut Creek, and in the 

 vicinity of Mount Diablo and called the beds in which it oc- 

 curred, Miocene. At Barker's Pass he mentions the presence of 

 Trophon ponderosum, and calls the beds Pliocene. 



In 1891, H. W. Turner 4 in his paper on the Geology of Mount 

 Diablo refers to the localities at Kirker's Pass, Corral Hollow and 

 Railroad Ranch. Collections of fossils were made and the fossil 

 leaves were turned over to Ward and Lesquereux for identifica- 

 tion. A part of these were considered as belonging to the Plio- 

 cene and a part to the Miocene. The most important evidence 

 for referring the San Pablo to the Pliocene he considers to be 

 the character of the tuff and conglomerates which are made up 

 chiefly of detrital material of hornblende and pyroxene ande- 

 sites. These eruptions were considered to have taken place in 

 Pliocene time. The andesitic material at Kirker's Pass was con- 

 sidered probably to have been derived from volcanic areas to the 

 north of San Pablo Bay. He concludes that these localities are 

 of Pliocene age notwithstanding the Miocene aspect of a part of 

 the flora. 



In 1895, Mr. George H. Ashley in his paper on the Neocene 

 Stratigraphy 5 of the Santa Cruz Mountains in California, 

 mentions fossiliferous transitional beds south of Half Moon Bay 

 which lie conformably upon the Monterey and beneath the 

 Merced. These beds became known later as the Purisima. 

 AVhether they are the ecpiivalent of the San Pablo or not, is not 

 certain. 



In May, 1898, Professor J. C. Merriam in The Distribution 

 of the Neocene Sea-Urchins of Middle California gives a de- 

 scription of the San Pablo formation in the San Pablo Bay 

 section, and correlates it with the beds at Kirker's Pass. He 

 states that "at all of the localities at which the San Pablo is 

 known, it is characterized faunally by the presence of a peculiar 

 assemblage of genera and species in which Astrodapsis is the 



3 Geol. Surv. of Calif. Palaeontology, vol. 2, p. 109. 

 i Bull. Geol. Soe. Amer., vol. 2, p. 383. 



5 Proc. Cal. Acad. Sc., 2d Ser., vol. 5, pp. 273-367. 



6 Bull. Dept. Geol. Univ. Calif., vol. 2, no. 4, pp. 109-118. 



