366 University of California Publications in Geology [Vol. 9 



the Eocene of this coast. The stratigraphy and fauna of the Tejon 

 is far better known than that of the Martinez. This is due to the 

 somewhat greater distribution of the Tejon, its more abundant and 

 better preserved fauna and to a well-marked constancy in certain 

 phases of its lithology over all California. Stratigraphy alone is 

 powerless in many cases to settle the structural features, as uncon- 

 formable contacts with marked differences of dip and strike are gen- 

 erally cloaked ; again, that many times there is only a diseonf ormity 

 between two formations very different in age is a common experience 

 of the field geologist working in California. Lithology is very helpful 

 at times, but great danger arises when correlation or even extended 

 mapping is based upon this alone. Every device must be used in our 

 efforts to solve the intricate questions arising in connection with the 

 sedimentary formations, and among these, the careful determination 

 of fossils and study of the related faunas is not the least. Here, as 

 elsewhere, mistakes occur and to avoid them a thorough study of the 

 faunas of the various groups is necessary. This paper will attempt 

 to aid the geologist and palaeontologist to separate sharply the Tejon 

 from the Martinez by describing the faunal differences as well as the 

 lithological and structural ones. 



The Tejon group is a unit both stratigraphically and faunally. 

 Minor stratigraphic breaks may occur at various horizons within the 

 group, but when these are evaluated by faunal studies they have 

 been found to be of minor importance in all cases. From the lower- 

 most horizon to the uppermost the faunas do not appear to be sepa- 

 rated sharply, and many species range throughout the entire thick- 

 ness of the Tejon. Very gradual changes in faunas, however, do 

 occur and the writer recognizes four faunal zones in the Tejon group 

 of California. These zones are, in ascending order, the Turbinolia 

 zone, the Rimella simplex zone, the Balanophyllia variabilis zone, 

 and the Siphonalia sutterensis zone. Of these the first three are 

 present in the San Francisco Bay region. The uppermost is typically 

 exposed in the Marysville Buttes, which are located in the center of 

 the Sacramento Valley, and at several places along the eastern border 

 of the Great Valley, on the western flanks of the Sierra Nevada. 

 This zone may also be present in the Coalinga region. Its absence 

 in the Mount Diablo section is probably due to post-Tejon and pre- 

 Oligocene erosion, as there is a strong suggestion of unconformity 

 between the Oligocene, the Agasoma gravidum zone and the Tejon 

 at Walnut Creek. The Tejon is found in general to rest with distinct 



