68 



University of California Publications. 



[Geology 



origin while Member D is undoubtedly marine and so we would 

 expect it to be more uniform in thickness than the lower members. 



Parts of the member are much harder than others and form 

 prominent ridges all along the northern and western slopes of 

 La Brea Ridge. One bed, about 30 feet thick, forms one 

 continuous vertical wall from the eastern end of La Brea canon 

 around the Pescadero Creek. This bed is extremely fossiliferous 

 in parts, in certain places being almost entirely composed of 

 fossil remains. The following species were identified : 



Pecten ashleyi Tresus nuttalli 



Pecten oweni Mulinea densata 



Ostrea, sp?. In great abundance. My a, sp? 

 Mytilus, sp? Tapes, sp? 



Mytihis, n. sp. Standetta nasuta 



Cardium, sp. Macoma nasuta 



Cardium blandum Crepidula princeps 



Area trilineata Prupura, sp? 



Macoma nasuta Drillia, sp? 



Pectunculus septentrionalis Balanus, sp? 



Panopea generosa 



Member E. — This member is about -±00 feet thick and con- 

 sists of coarse sandstone usually brown, but on close inspection is 

 seen to have a slight bluish tinge. This bed becomes exceedingly 

 coarse and conglomeratic at the top. Prominent outcrops show 

 cavernous weatherings to a marked degree. This feature is 

 believed to be characteristic of the uppermost San Pablo beds 

 elsewhere. This upper division of the San Pablo formation is 

 not as fossiliferous as member D nor do the fossils extend to 

 the top of the series. Certain fine-grained layers of this member 

 are exceedingly gritty to the touch, and it is probable that 

 volcanic ash enters into their composition. 



General Features of the San Pablo Formation. — The San 

 Pablo formation as mapped in this region occupies a broad 

 synclinal basin over the central part of the area. The floor 

 of this basin is for the most part Monterey shale but this floor 

 has been deformed in the post-San Pablo uplift. The outlying 

 areas of the basal conglomerates were evidently laid down in 

 the same sedimentary basin, but the whole basin has suffered 

 differential movement and so the dips and strikes of the beds 



