1916] Dicker son: Tejon Eocene of California 423 



graphy and referred a portion of the Eocene strata to the Martinez. 

 His description of the stratigraphic sequence is as follows : 



To Messrs. Stanton, Merriam, Weaver and Dickerson is due the credit 

 of demonstrating in the Mount Diablo region the existence below the 

 Tejon of a series of beds of Eocene age, which is clearly distinguishable 

 from that terrane by its characteristic fauna and unconformable relation- 

 ship. This has been named the Martinez, but only meager accounts of 

 its stratigraphy are available and its existence was recognized at only a 

 few localities. 



Our work now proves that this lower member of the Eocene is of 

 very considerable extent southward on the west side of San Joaquin 

 Valley; that it consists of three or more clearly denned members, and 

 that, in addition to the unconformity already described between it and 

 the Cretaceous, there also exists a decided unconformity between it and 

 the overlying Tejon. 



The Martinez is well developed in Townships 17 and 18 South, Ranges 

 13 and 14 East, in the Salt Creek-Cantua region, and comprises a basal 

 bed of chocolate sands with glauconitic sands overlain by yellow sands 

 and conglomerates and these overlain in turn by other chocolate shales. 

 The generalized section of the Martinez in this particular area may be 

 stated as follows: 



3. Upper chocolate shales comprising bluish shales at top, grad- 

 ing down into chocolate or brown shales which weather 

 to clays. 



These rest upon other chocolate shales which become 

 sandier toward bottom. These shales vary in thickness. 



600-900 ft. 



2. Yellow sand and conglomerate. 



Bluish sandy shales and thin sandstone, variable in thick- 

 ness. 200 ft. 

 Massive yellow sandstone with large dark brown segrega- 

 tions and concretions and some layers of bluish sandy shale. 

 Fine sand with local beds of conglomerate interbedded with 

 blue and brown shales; a considerable amount of glauconitic 

 material at base. 300 ft. 



1. Lower chocolate shales. 



Beds of chocolate and brown shale with small ferruginous 



and limy concretions and layers of glauconitic sands. 1000 ft. 



2,700 ft. 



Dumble lists species collected "from the top of the lower chocolate 

 shales at a locality on Salt Creek in the SW % of NW Section 25, 

 Twp. 18 S, R. 14 E." 



The greatest surface exposure of these beds in this area is found in 

 Twp. 17 S., R. 13 E., where except for a band of Cretaceous along the 

 south line they form the surface rocks for the entire southern half of the 

 township. The exposure of the lower shale is only a half to three- 

 quarters of a mile in width and the upper shale occupies a similar belt, 

 but the yellow sandstone member has an average breadth of exposure 

 of nearly two miles. On the eastern line of this township this is narrowed 



