1914] Dickerson: Fauna of the Martinez Eocene of California 



65 



fine outcrop of compact bluish sandstone occurring on the west side of Alhambra 

 Valley, and near the top of the Chico, the writer found an abundance of fossils, 

 characteristic of this group. . . . From this point to the east and west the 

 structure of the strata is anticlinal, showing an apparently conformable series 

 up as far as the Miocene on each side. 



From the standpoint of stratigraphy, one would hardly be disposed to find 

 fault with Gabb's conception of the Martinez, since in this, the typical locality, 

 the Chico, Martinez, and Tejon appear everywhere to be conformable, while 

 numerous complications of the stratigraphy have still farther increased the 

 difficulty of separating these three groups on stratigraphic grounds. 



Lithologically there are some differences between the Martinez and the 

 adjoining formations, the most important of which are the slightly different 

 aspect of its sandstones and the frequent presence in them of considerable 

 quantities of glauconite. The sandstones are often grayish, differing from the 

 yellowish or bluish rocks of the Chico and the massive white to dull red Tejon 

 sandstones. In many places the Martinez contains large quantities of glauconite 

 disseminated evenly through the sandstone in rounded grains of considerable 

 size. Glauconite does not seem to occur at all in the Chico but may possibly 

 be found toward the base of the true Tejon. The truly glauconitie rocks belong 

 principally to the Martinez. 



While the group shows little which would serve to separate it strati- 

 graphically or lithologically from the over and underlying formations, its 

 fauna, on which Gabb based his classification, contains numerous elements 

 throwing light on its geologic relations. Between the Chico-Cretaceous and 

 the Miocene there are two distant faunas present, viz., the Martinez (in part) 

 and Tejon of Gabb, or the Lower and Upper Tejon of Mr. Stanton. As other 

 criteria failed to separate satisfactorily the Chico, Martinez, and Tejon, exten- 

 sive fossil collections were made by the writer at all possible points. 



Merriam then discussed collections made in a section across the 

 strike in the typical Chico, Martinez and Tejon, suggested the exist- 

 ence of two faunal zones in the Martinez, and described the palaeon- 

 tology of the Martinez : 



The faunas, though overlapping, are in the main quite distinct, and no 

 great difficulty has been experienced by the writer in separating the groups on 

 this basis. While some intermingling of species exists, it is not greater than 

 we should expect to find in adjoining groups or periods. It should also be 

 observed that the beds with a Tejon-like Martinez fauna and those containing 

 an assemblage of characteristic Tejon forms are comparatively close together. 

 The change from one fauna to the other may possibly have taken place in a 

 short time by migration, but we can not assert positively as yet that the 

 apparent conformity of the beds is a real one; sedimentation may have been 

 interrupted between the times of deposition of the 'two groups. It is, at any 

 rate, quite clear that the two sets of strata, or two faunas, while belonging 

 perhaps to the same series, represent different periods in the geological history 

 of California, periods quite as distinct, so far as faunal evidence is concerned, 

 as the Miocene and Pliocene, or the Pliocene and Quaternary. The upper 

 division of this series has already, on the grounds of its characteristic fauna, 

 been named the Tejon. To a mixed group of rocks, to which the fauna here 

 called the Martinez gave individuality, the name Martinez group was applied 



