Clark: The San Lorenzo Series of Middle California 77 



ness of the beds below the Claremont shale down to the Tejon being 

 less than one hundred and fifty feet ; on the south side, the thickness 

 of the beds in the corresponding - section is nearly five hundred feet. 

 The difference in thickness of the San Lorenzo beds on the two sides of 

 the anticline is apparently due to erosion. This is borne out by the 

 fact that along this line there is a slight difference in strike between 

 the beds of the two horizons, six to eight degrees, and that only a 

 short distance to the northwest of the locality on the north side of 

 the anticline mentioned above, less than a half-mile, the San Lorenzo 

 beds are entirely absent ; the basal Monterey beds here rest directly 

 upon the Eocene. At Selby Station on San Pablo Bay (Napa Quad- 

 rangle), about six miles to the northwest of this locality, the basal 

 beds of the Monterey (Area montereyana zone) rest with a marked 

 unconformity upon the Martinez (Lower Eocene). In the Berkeley 

 Hills to the west and southwest of the Sobrante anticline, a distance 

 of less than four miles, the Monterey rests directly upon the Chico 

 (Upper Cretaceous), deposits of the Eocene and Oligocene periods 

 being absent. 



SAN LORENZO SERIES OE THE SAN RAMON SYNCLINE 

 General Statement 



The San Lorenzo section of the San Ramon syncline is considerably 

 different from that just described. Only one distinct formation was 

 recognized ; this is called the San Ramon, the name already applied 

 to the basal member of the San Lorenzo of the Sobrante anticline. 

 Outcrops of the San Ramon formation are found on both sides of the 

 southeast plunging, closely folded, overturned San Ramon syncline. 

 Here the formation rests upon the Tejon (Eocene), being separated 

 by a questionable disconformity, and is overlain disconformably by 

 beds containing the fauna of the Area montereyana zone (Miocene). 

 The beds on the west side of the syncline dip about sixty-five degrees 

 to the east with a strike of about twenty degrees west of north ; on 

 the east side of the syncline the strike is about north fifty degrees 

 west, while the dip, due to the fact that the strata here have been 

 overturned, is sixty or seventy degrees to the east. 



It seems very probable that the San Ramon formation of this 

 section represents a longer period of deposition than the San Ramon 

 formation of the Sobrante anticline, but whether the time of the 

 deposition of the Kirker tuffs and the Concord formation are repre- 



