Clark: The San Lorenzo Series of Middle California 55 



species which are undoubtedly very closely related. On the other 

 hand, the fauna which is found in beds classed as Upper Oligocene. 

 the Acila gettysburgensis zone, 4 has a somewhat similar relationship 

 to that found in the Monterey or Vaqueros, Lower Miocene. How- 

 ever, when these faunas, forming the Upper and Lower Oligocene as 

 recognized on the West Coast, are compared, they apparently show 

 a much greater similarity to each other than does the one to the 

 Eocene and the other to the Lower Miocene. 



So little direct evidence is there as to the Oligocene age of these 

 western beds that the writer is tempted to raise the question as to 

 whether or not at least a certain portion of them might not be 

 Upper Eocene. It is generally held by those who are familiar with 

 the fauna of the Tejon, Upper Eocene of the "West Coast, that it 

 does not represent the uppermost Eocene as recognized in the Gulf 

 region to the east, that is, the Jaeksonian. Thus, on the West Coast 

 there is a time interval which apparently is not accounted for and the 

 thought naturally suggests itself, why might it not be that the fauna on 

 the West Coast that is referred to the Oligocene is in reality, at least in 

 part, Upper Eocene ? There is a number of facts that could be used 

 in support of this contention. However, the work of describing the 

 faunas of the Eocene, Oligocene and Miocene of the West Coast and 

 of establishing the proper sequence and stratigraphic relationships has 

 only begun ; this is especially true of the so-called Oligocene. It is 

 for this reason that no attempt is made to discuss in detail the possible 

 general correlation with the eastern and European sections. The 

 writer believes that the chief contribution of this paper, outside of 

 describing the fauna of the San Lorenzo as found in the vicinity of 

 Mount Diablo, is the establishment of the stratigraphic relations of 

 these so-called Oligocene beds in California and their correlation with 

 the Oligocene as found in Oregon, Washington and British Columbia. 



The name San Lorenzo series is applied, in this paper, to all of 

 the known marine beds, which in California, Oregon, Washington and 

 British Columbia have generally been referred to the Oligocene ; this 

 is synonymous with the name, Astoria series, as used by Arnold and 

 Hannibal, 5 and to the Clallam formation, the name recently applied 

 by Weaver" to the marine Oligocene of Washington. 



* The Upper Oligocene, Acila gettysburgensis zone, at the present time is known 

 for a certainty only in Oregon, Washington and British Columbia. 



5 Arnold, Ralph, and Hannibal, Harold, The marine Tertiary stratigraphy of 

 the North Pacific Coast of America, Proe. Amer. Philos. Soc, vol. 52, pp. 576-578, 

 1913. 



e Weaver, C. E., The Tertiary formations of Western Washington, Wash. Geol. 

 Surv., Bull. 13, p. 16(1, 1916. 



