Clark: The San Lorenzo Series of Middle Calif or nut 107 



throughout the state, such as Vaqueros, Temblor and Monterey, all 

 belong to the same general period or cycle of deposition and ought 

 to be referred to under one general name, "Monterey series." It 

 should also be remembered in this connection that the beds of the 

 San Lorenzo formation of the type section, are described as apparently 

 grading up into the Vaqueros. The following statement is found in 

 the Santa Cruz Folio : ' ' The Vaqueros in general lies conformably 

 above the San Lorenzo formation, and there is often a gradual change 

 from one formation to the other, with no clear line of demarcation 

 between them. ' ' 84 



To sum up : At the present time, it is the belief of practically all 

 geologists who are familiar with the marine Upper Tertiary deposits 

 of the West Coast, that the Turritella ocoyana and Turritella inezana 

 beds belong to one general period of deposition. As yet no evidence 

 has been brought forward that they are separated by a stratigraphic 

 break. Also, it has been the belief of Ralph Arnold, who first recog- 

 nized marine Oligocene in California, that certain beds in the Santa 

 Cruz Mountains between the San Lorenzo and the Vaqueros contained 

 a transitional fauna and that there was no stratigraphic break between 

 the San Lorenzo and Vaqueros of that section. With the above facts 

 in mind, we will review the evidence as to the faunal relationship of 

 the two horizons, the Oligocene and Lower Miocene. 



The first question that must be answered before attempting to 

 establish the general relationship of the Oligocene to the Lower 

 Miocene is — What is the relationship of the beds of the Turritella 

 ocoyana zone to those of the Turritella inezana zone? Is the fauna 

 of the latter horizon, as suggested by J. P. Smith, the shallow-water 

 equivalent of the fauna of the San Lorenzo of the Santa Cruz Moun- 

 tains ? 



The writer has already, in a former paper, 85 expressed the opinion 

 that future work will show that the fauna of the Turritella inezana 

 zone is more closely related to that of the Turritella ocoyana zone 

 than to the fauna of the Agasoma gravidum zone. This opinion is 

 based upon the fact that a large number of species is known to be 

 common to the first two zones, while very few species are known to 

 be common to the third zone and either of the other two. Very few 

 forms which might be considered good horizon determiners are found 



Brainier, J. C, Newsom, J. F., and Arnold, Ralph, IT. S. Geol. Surv., Santa 

 Cruz Folio 163, p. 4, 1909. 



85 Clark, B. L., The occurrence of Oligocene in the Contra Costa Hills of 

 Middle California, Univ. Calif. Publ., Bull. Dept. Geol., vol. 9, no. 2, p. 16, 1915. 



