1915] 



Clark: Fauna of the San Pablo Group 



399 



strike of the San Pablo Beds." Later work shows that the Monterey 

 shale, mapped as striking in under the San Pablo, in reality turns and 

 may be traced back around the nose of the steeply-plunging anticline 

 that is found to the southeast of the San Pablo Bay syncline. See 

 map, plate 71. 



Relation to Pinole Tuff. — The San Pablo of the type section is 

 overlain by several hundred feet of basaltic tuffs. The lower beds of 

 tuff are quite coarse, containing considerable volcanic ejectamenta, 

 and appear to have been laid down very rapidly. The upper strata 

 are finer and are distinctly bedded. Clay beds are interbedded with 

 the tuff. The Pinole Tuff appears to have been laid down, in part at 

 least, under water as the casts of fresh-water shells are quite abundant. 



The stratigraphic relationship of the Pinole Tuff to the San Pablo 

 Group in this immediate vicinity is unconformable, as shown by an 

 irregular contact and a slight difference in strike. 



Detailed Section of the San Pablo Group, as Measured on the North Side 

 of the San Pablo Bay Syncline 



Pinole Tuff. 



(Unconformity.) 

 San Pablo 



Division B Feet 

 Coarse gray sandstone 129 

 Thin layer of pink shale 



Coarse gray sandstone 66 

 Coarse gray, cross-bedded, tuffaeeous sandstone, bedded with thin 

 layers of clay; contains Miclinia densata and Tivela gabbi 211 

 Medium fine sandstone; toward bottom grades into shale 106 

 Heavy, massive, coarse sandstone with lentils of harder and 



darker sandstone; very f ossiliferous 34 

 Gray, medium fine sandstone 28 

 Coarse, massive, gray sandstone with lentils of harder and darker 

 sandstone; contains Astrodapsis tumidus. Pinna alamedensis, 

 Trophon carisaensis, etc. 75 

 Pearl-gray shale 



Medium fine, gray sandstone; contains Trophon lawsoni, Astro- 



dapsis tumidus and Mulinia pabloensis 250 

 Medium fine, gray sandstone 225 

 Coarse gray, conglomeratic, tuffaeeous sandstone 115 

 (Irregular contact.) 

 Division A. 



Medium fine, yellowish gray concretionary sandstone; contains 



Pitaria behri, Pitaria stalderi 140 



Layers of coarse fossiliferous sandstone alternating with medium 

 fine to coarse, massive, unf ossiliferous layers of sandstone; 

 Scutella gabbii found in the lower 250 feet, Astrodapsis tumidus, 

 subsp. cierboensis, and Scutella pabloensis, in the upper 500 feet 765 



Monterey. 



2234 



