1915] 



Clark: Fauna of the San Pablo Group 



441 



good faunal evidence to show that both the Lower San Pablo and 

 Scntella breweriana zone belong to a later horizon than the Temblor 

 and Merychippns zone. During the time represented by the uncon- 

 formity between the Temblor and Santa Margarita of this district, 

 beds belonging to the Scutella breweriana zone and the Lower San 

 Pablo were being deposited. 



It will be very readily seen that the determination of the Upper 

 Temblor as Middle Miocene has a very important bearing on the age of 

 the San Pablo and of the Scutella breweriana zone. The lower limit 

 of the latter can probably not be below upper Middle Miocene. The 

 San Pablo being younger than the Scutella breweriana zone may pos- 

 sibly have its lower limit near the lower part of the Upper Miocene. 

 However, it must be admitted that this determination of the lower 

 limit of the San Pablo is rather indefinite, first, because we are not 

 certain of the relation of the Scutella breweriana beds to those of the 

 Lower San Pablo; second, because at present it is impossible to esti- 

 mate the length of time represented by the hiatus between the beds of 

 the Temblor and the Scutella breweriana zone. 



The best evidence that we now have as to the age of the uppermost 

 beds of the San Pablo is also derived from land vertebrate fossils. The 

 writer has already shown that the fauna of the Etchegoin is distinctly 

 younger than that of the San Pablo. In the region of Oilfields, Fresno 

 County, California, immediately to the north of Coalinga, the Santa 

 Margarita, which here is equivalent to that of the Upper San Pablo 

 of Middle California known as the Astrodapsis whitneyi zone, is over- 

 lain unconformably by about 1800 feet of beds which have been re- 

 ferred questionably by Arnold and Anderson 47 to the Jacalitos Forma- 

 tion. No invertebrate species have been obtained from these beds and 

 there is a question as to their exact correlation with the known marine 

 horizons. This fact is to be noted, however, that these 1800 feet of 

 strata lie unconformably above the Santa Margarita and are below the 

 type section of the Etchegoin, the latter of which was considered by 

 Arnold to be Miocene in age. In the lower beds of the Jacalitos ? ver- 

 tebrate remains were found by the University of California party 

 referred to above. Professor Merriam from this vertebrate evidence 

 believes that the Lower Jacalitos? is near the age of the Rattlesnake 

 or Thousand Creek beds which are referred to the early Pliocene. 



The problem is complicated at this point by the fact that we do 

 not have marine invertebrates associated with the vertebrates found 



*t Bull. U. S. G. S., 398, p. 107, 1910. 



