Vol. 6] 



Diclcerson: Martinez Formation. 



175 



The Martinez formation is represented areally by a strip 

 averaging one quarter of a mile wide which extends from Lower 

 Oil Creek westward for four miles. Its west end is terminated 

 by a cross-fault, while its eastern end is cut off by the Tejon 

 conglomerate. 



Throughout the area studied there is a constant difference in 

 strike between the Martinez and the Tejon. This is generally 

 at least ten degrees, and in lower Oil Canon it is much greater. 

 This difference in strike causes the Tejon conglomerate to rest 

 upon a stratum of hard Martinez sandstone at one locality and 

 upon soft Martinez shales at another, which sufficiently accounts 

 for a very irregular Martinez-Tejon contact. In lower Oil 

 Canon, a mile southeast of Stewartville, a basal conglomerate 

 of the Tejon formation has a strike of N45°W, while only a 

 hundred feet away Martinez sandstone is found with a strike of 

 N 90° W. There can he no doubt about the age of the sand- 

 stone as it contained the following characteristic species at this 

 locality: Heteroderma, sp., Trococyatlius zitteli, Tellina unduli- 

 fera, Urosyca can-data, Pectunculus veatchii, var. major, Nep- 

 tnnca mucronata. 



Professor Louderback, who has worked extensively in the Mt. 

 Diablo quadrangle, has found Tejon fossils in the sandstone a 

 few feet above and conformable with the conglomerate, so that 

 the age of the conglomerate is certainly Tejon. 



The dip of the Martinez throughout the field is greater than 

 that of the Tejon. The basal Tejon conglomerate, which is from 

 ten to twenty feet thick, rests upon the Martinez sandstones and 

 shales and forms a \vell-defmed bed for over four miles in length. 

 It consists of very coarse pebbles and boulders, which make it 

 easily separable from the sandstones of the Martinez. The 

 pebbles and boulders are in most places quartzose, but fragments 

 of fossiliferous limestone, and sandstone and igneous rocks of 

 various kinds also occur. Nucula truncata, Cylichna costata, 

 Modiola cylindrica ( ?), Dentalium cooperi, and Zirphaea ( .') 

 bored boulders which resemble very closely the ZirphaSa{ '!) 

 borings on the Martinez-Chico contact described below, have been 

 obtained from limestone and sandstone boulders imbedded in the 



