414 University of California Publications in Geology [Vol. 8 



In this region, the Orinclan rests directly on the San Pablo, the 

 Pinole Tuff being absent. 



FAUNA 



The fauna found below the limestone on Rocky Ridge is to be cor- 

 related with that of division A of the San Pablo Bay section and of the 

 Mount Diablo section. Scutella gabbii and Astrodapsis tumiclus subsp. 

 cierboensis have not been found here, but in the section on Las Trampas 

 Ridge, about a mile to the north, these two species occur in their 

 proper stratigraphic sequence. On Rocky Ridge the following species 

 were found below the limestone, and are believed to be characteristic 

 of the lower San Pablo: Spisula abscissa, Mytilus coalingensis, n. var? 

 and Ostrea bourgeoisie. 



Above the limestone, a fairly large fauna was obtained associated 

 .with Astrodapsis ivhitneyi. Some of these are Amiantis dalli, Cyrena 

 calif ornica, Mytilus trampasensis, Mytilus perrini, Macoma pabloensis, 

 Mya dickersoni, Venus martini, Cancellaria pabloensis, Natica 

 (Neverita) aruoldi, Trophon carisaensis. See localities 38, 39, 41 and 

 1224. 



Tice Valley Syncline 



STEATIGEAPHY AND LITHOLOGY 



A good section of the San Pablo is found north of Las Trampas 

 Ridge in the vicinity of Tice Valley, Contra Costa County, where it 

 is a little over twenty-one hundred feet thick. The beds outcrop on 

 both sides of a syncline, and are overlain by the Pinole Tuff and the 

 Orinclan Series. 



Relation of San Pablo to Monterey Group. — In this section the San 

 Pablo apparently grades downward into the Monterey, the beds of the 

 two formations having the same dip and strike. The upper Monte- 

 rey is composed of medium fine, yellow-brown sandstones, which are 

 very much like those of the upper Monterey of the Rocky Ridge section. 



Lithology. — On account of insufficient collecting localities in this 

 area no attempt has been made to draw a definite line, corresponding to 

 that between division A and B on the south side of Mount Diablo or 

 on the bay. 



