108 University of California Publications in Geology [Vol. ll 



common to the faunas of the two Turritella zones and the Oligocene 

 fauna, either as known in California or in Oregon and Washington. 



J. P. Smith, in his paper entitled "Geologic range of Miocene 

 invertebrate fossils of California," 80 listed one hundred and seventy- 

 three species of invertebrates from the Lower Miocene of California. 

 A number of these belong to the Agasoma gravidum fauna and should 

 be eliminated. Considerable work has been done on the fauna of 

 the Lower Miocene since Smith's paper appeared, and at the present 

 time over two hundred species are known from that general horizon. 

 Smith listed fifty-six species from the "Vaqueros, " Turritella inezana 

 zone, only ten of which are confined to that zone, twenty-five species, 

 or nearly half, going into the Turritella ocoyana zone but not higher, 

 ten per cent of this fauna being composed of Recent species. 



Out of the one hundred and thirteen determinate species in the 

 San Lorenzo series of the Mount Diablo region, only thirteen extend 

 into the Lower Miocene (T. inezana and T. ocoyana zones) or higher 

 horizons ; of these, several are only compared with species in the 

 Miocene. Only eight species of the Sah Lorenzo series extend into 

 the Lower Miocene beds of the California province. Contrasting this 

 witli the much larger number of species common to the San Lorenzo 

 series of the Mount Diablo region and the Oligocene of Oregon, 

 Washington and British Columbia (thirty-nine), it will readily be 

 seen how much closer is the relationship in the latter cases than in 

 the former. 



Again, the distinctness of the fauna of the San Lorenzo series 

 from that of the Lower Miocene is shown in the greater number of 

 Recent species in the latter than in the former; according to Smith, 

 ten per cent of the fifty-six species known from the Turritella inezana 

 fauna are Recent. In the San Lorenzo beds of the region of Mount 

 Diablo, out of one hundred and thirteen determinable species, only 

 two are Recent, less than two per cent. The writer's conclusion from 

 these data is, that there is a large faunal break between the Lower 

 Miocene and the Oligocene of California, and that this break is prob- 

 ably a general one. 



The existence of a time hiatus between the fauna of the Lower 

 Miocene and that of the Oligocene is substantiated by the presence 

 of a general stratigraphic break. Crustal movements, of considerable 

 magnitude in places, turned up the Oligocene beds so that when the 

 Miocene sea encroached upon the area that had been exposed to 



86 Smith, J. P., Proc. Calif. Acad. Sci., ser. 4, Geol., vol. 3, p. 164, 1912. 



