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University of California Publications. 



| Geology 



that the sharp separation of the Martinez fauna from that of 

 the Chieo and Tejon indicated that an unconformity certainly 

 existed between the Martinez and Chico, and that sedimentation 

 might have been interrupted between the times of deposition of 

 the Martinez and the Tejon. 



In the work on the Martinez formation carried on in past 

 years by Gabb, Stanton, Merriam, and Weaver, 4 no locality was 

 found at which the stratigraphic relations of this formation to 

 the Chico and Tejon were clearly shown. 



During the fall term of 1910, while working under the direc- 

 tion of Dr. Merriam, in a small area four miles north of Mt. 

 Diablo, the writer has been fortunate enough to find a section 

 in which the Martinez-Chico and Martinez- Tejon contacts are 

 well exposed, and the Martinez seems clearly separated by un- 

 conformity from both the Chico and the Tejon. "While this 

 condition may be only local, it is interesting to find evidence of 

 considerable time-intervals both preceding and following the 

 deposition of the Martinez. The faunal relations between the 

 Chico and the Martinez also illustrate strikingly the interruption 

 of sedimentation. 



NATURE OF CHICO, MARTINEZ, AND TEJON FORMATIONS IN 

 THE AREA CONSIDERED. 



The Chico formation in this region consists of a hard, dark, 

 fine-grained sandstone with subordinate strata of dark gray 

 limestone, which is interbedded with a shale and a soft buff sand- 

 stone containing numerous fragments of leaves and stems. It 

 has a general east and west strike and dip of 60°-70° N, and 

 contains a characteristic Chico fauna including Meckia sella, 

 I non ramus, sp., Venus varians, Mytilus, sp. (near quadratus), 

 Tellina mathewsoni, Pugnellus manubriatus, Cinulia obliqua, 

 Helicoceras vermicular is, Aneyloceras, sp. 



The Martinez comprises a blue-gray, glauconitic sandstone 

 and a sandy shale with thin strata of limestone. It has a general 

 east and west strike and a dip varying from 35°-50° N. The 



* Weaver, C. E., Contribution to the Palaeontology of the Martinez 

 Group, Univ. Calif. Publ. Bull. Dept. Geol., vol. 4, pp. 101-123, 1905. 



