1915] 



Clark: Fauna of the San Pablo Group 



389 



HISTOKICAL REVIEW 



The first general description of the geology in the vicinity of San 

 Pablo Bay was made by Dr. J. S. Newberry in 1855. 1 The deposits 

 were correlated with the "sandstone of San Francisco" described 

 on page eleven of the same volume. The Cretaceous. Eocene, Miocene, 

 and Pliocene were included in the same series and designated as 

 "Miocene or more recent." A fairly detailed description was given 

 of a portion of this section, which is now recognized as belonging to 

 the upper part of the San Pablo Group in the type section. Under the 

 heading "Pecten Beds," Newberry makes the following statement: 



My attention was first called to the fossiliferous beds by noticing a stratum 

 which may perhaps be called a shell limestone about four feet in thickness, 

 which is composed almost exclusively of peotens. From its superior hardness 

 it had resisted the action of the waves, which had cut deeply into the softer 

 strata, and stood out like a wall, breast high, and running like a reef, far out 

 into the shallow waters of the bay. 



To one who is familiar with the east shore of San Pablo Bay, this 

 locality can be easily recognized. It is less than one-fourth of a mile 

 to the west of the town of Eodeo on the south side of Lone Tree Point. 

 It was from these beds that the type of Pecten pabloetisis Conrad was 

 obtained. One other Pecten was found here which was described as 

 being more than six inches in diameter. This was probably Pecten 

 crassicardo Conrad, which occurs at this horizon. 



Doctor Newberry also recognized and described, fairly accurately, 

 the Pinole Tuff which, in this section, overlies the San Pablo. 



The first writer to differentiate beds referred to the San Pablo 

 Group, from the underlying Monterey (also Miocene) was Professor 

 J. D. Whitney, 2 who in 1865 recognized the division on the north side 

 of Mount Diablo, but not in the vicinity of San Pablo Bay. The 

 upper beds (San Pablo, Pinole Tuff and Orindan) were referred to 

 the Pliocene, the lower (Monterey Group), to the Miocene. 



Whitney described the beds on the north side of Mount Diablo as 

 follows : 



Rocks of both Pliocene and Miocene age are extensively developed to the 

 north of the strata just spoken of on the northern slope of the range in which 

 are the coal mines. Those which we refer to the Miocene division of the 

 Tertiary consist chiefly of sandstones which are very heavy bedded toward the 



i Pac. R. R. Report, vol. 6, pp. 13-14, 1855. 

 : Geol. Survey Calif., vol. 1, p. 31, 1865. 



