Clark: The San Lorenzo Series of Middle California 105 



oldest Oligocene faunas in these northern localities, that is, the fauna 

 of the Molopophorus lincolnensis zone and that of the Sooke beds. 



RELATION OF FAUNA OF THE SAN LORENZO SERIES TO THAT OF 

 THE LOWER MIOCENE 



By Lower Miocene in California, as the term is used in this paper, 

 is meant those formations generally described under the names 

 Vaqueros, Temblor and Monterey. It is the writer's conclusion that 

 the fauna of the San Lorenzo series, as described in this paper, is 

 older than that of the lowest horizon that is generally referred to the 

 Lower Miocene, and also that a general stratigraphic and faunal break 

 exists between these horizons. The evidence for this statement will 

 be brought out in the following paragraphs. 



Two somewhat different faunas have been recognized in the Lower 

 Miocene; one is known as the fauna of the Turritella ocoyana zone, 

 the other, of the Turritella inezana zone, mentioned above. The first 

 to suggest that the fauna of the ' ' Turritella inezana ' ' zone was older 

 than that of the "Turritella ocoyana" zone was J. C. Merriam 75 in 

 his paper "A note on the fauna of the Lower Miocene." As has been 

 pointed out, Merriam correlated the fauna of the Agasoma gravidum 

 zone of Contra Costa County, the beds of which in the paper are 

 referred to the San Lorenzo series, with that of the Turritella ocoyana 

 zone, as known in the southern part of the state. Both the Turritella 

 ocoyana and Turritella inezana zones were referred to the Lower 

 Miocene. He believed it to be probable that the two faunas belonged 

 to the same general period of deposition. The following extract gives 

 his idea as to the possible conditions of deposition during Lower 

 Miocene time : 



When we come to study the subdivisions of the Lower Miocene both palaeonto- 

 logically and stratigraphically some interesting things relating to the movements 

 of the Miocene shore lines are suggested. The T. hoffmani^ zone is found prin- 

 cipally in the western or coast region. The T. ocoyana zone occurs in the western 

 region and also to the east of the Great Valley, where the T. hoffmani is not yet 

 known. It would therefore appear that the sea had not reached as far east in 

 the earliest Miocene as it did later, and that the thick shale beds over the lower 

 sands of the western region were formed while sandy T. ocoyana beds were being 

 deposited in the east. 



" Merriam, J. 0., Univ. Calif. Publ., Bull. Dept. Geol., vol. 3, no. 16, pp. 380- 

 381, 1904. 



?6 Turritella hoffmani Gabb equals Turritella inezana Conrad. 



