L6 



University of California Publications in Geology [Vol. 9 



For the purposes of this paper it will not be necessary to consider 

 the beds, which are above the stratigraphic break to which reference 

 has just been made. The beds below this unconformity (usually 

 designated as Lower Miocene) are known by various local names along 

 the Pacific Coast. It is still a question whether they form one, two, 

 or possibly more distinct epochs of deposition. In California two 

 faunal zones have been recognized in these beds, both of which repre- 

 sent a littoral facies of deposition. Besides these, there is a fauna 

 obtained from the diatomaceous shales of the Coast Ranges usually 

 known as the Monterey shale. This latter fauna has generally been 

 considered to be contemporaneous with the two littoral faunal zones. 

 However, in a recent paper Mr. F. M. Anderson 16 has expressed the 

 belief that the fauna from the Monterey shales of the Coast Ranges 

 belongs to a distinct and later period of deposition than either of the 

 two littoral faunas mentioned above. The lower of the two littoral 

 faunas has been generally known as the Turritella inezana zone ; the 

 upper as the Turritella ocoyana zone. Beds containing the fauna of 

 the lower zone have usually been called Vaqueros ; beds of the upper 

 zone have been referred to as Vaqueros, Monterey, and Temblor. 



The Agasoma gravidum beds of middle California were first pro- 

 visionally considered by Dr. J. C. Merriam 17 to be near the age of 

 the Turritella ocoyana beds, referred to above. With the data now 

 at hand, it would appear that the faunas of the Turritella ocoyana 

 and the Turritella inezana zones are more closely related than has 

 heretofore been supposed ; that though possibly there may be a strati- 

 graphic break between them, as has been reported in several localities, 

 the faunal evidence would seem to show that the time-break was 

 probably not a large one. There is apparently a much greater dif- 

 ference between the fauna of the Agasoma gravidum zone and that 

 of the Turritella inezana zone than there is between the fauna of the 

 latter and that of the Turritella ocoyana zone. It is certain that the 

 fauna of the Agasoma gravidum zone of Contra Costa County belongs 

 to an older horizon than the Turritella ocoyana zone, and it appears 

 to the writer to be older than the Turritella inezana zone. 



The fauna of the Area montereyana zone of Contra Costa County 

 is as old as that of the Turritella ocoyana zone and possibly older. 



is Anderson, F. M., and Martin, Bruce, Neocene record in the Temblor Basin, 

 California, and Neocene deposits of the San Juan District, San Luis Obispo 

 County, Proc. Cal. Acad. Sci., 4th ser., vol. 4, pp. 15-112, pis. 1-10, 1915. 



it Merriam, J. C, Fauna of the Lower Miocene in California, Univ. Calif. 

 Publ., Bull. Dept. Geol., vol. 3, p. 380, 1904. 



