3fesozo(c and Cce)iozoiG Geology and Palmontology. 87 



M. radiata, M. navis^ Area horni. A. gravida^ A. decurtata^ Cueullcea 

 matthewsoni., C truncata^ Axincea veatchi, A. sagittata, A. cor^ Lim- 

 opsis transversa, Pecten traski, P. operculifortnis, P. calif ornicus, 

 Lima microtis, L. appressa, Plicatula variata^ Ostrea breweri, Exo- 

 gyra parasitica, Terebratella obesa^ Flabellum remondianum, Tro- 

 chosmilia striata, Astroccenia petrosa, Ficus ma7nmillatus, now Fi- 

 copsis maynmillatus, Natica uvasana, Scalaria matthewsoni, Turri- 

 tella infra-granidata, Uhione angulata, now Callista angulata. Tapes 

 cretacea, Cardita veneriformis, Yoldia nasuta, Placunanomia inor- 

 nata; from Siskiyou Mountains of Oregon, /S'i7zg?f« oregonensis^ Tell- 

 ina whitneyi, Dosinia pertenuis, Modiola siskiyoiiensis, now Volsella 

 siskiyouensis, aud Ostrea malleiformis . 



In 1865, J. D. Whitnej^* described the Contra Costa Hills, which 

 consist of a subordinate group of elevations, lying west of Martinez 

 and the San Ramon and Livermore Valleys, and extend through Contra 

 Costa county into Alameda and Santa Clara, aud finally become 

 mero-ed in the Mount Hamilton division of the Monte Diablo Rano-e. 

 They are made up of Tertiary and Cretaceous strata, usually but little 

 metamorphosed, although a belt extending along their western side is 

 considerabl}' altered from its original character. 



Beginning at the northwest extremitj^ of the group at Martinez, we 

 have in the immediate vicinity of that place Cretaceous strata, well 

 exposed in the bluffs along the Straits of Carquines. Here the rocks 

 observed are sandstones, shales and argillaceous limestones, the latter 

 foi-ming bands and lenticular masses in the shales, generally but a 

 few inches thick, although sometimes as much as three feet. Their 

 strike is usualh^ about N. 42° W, varying, however, from N. 39° W, to 

 N. 44° W, and they dip southwest at an angle of from 35° to 60°. The 

 rocks near Martinez have furnished a great many species of fossils. 



In passing along the shore of the Straits of Carquines, west of Mar- 

 tinez, the Cretaceous strata occur for about seven miles, and are made 

 up of shales and sandstones, the former containing frequent thin la3^ers 

 of hydraulic limestone. These rocks exhibit but few fossils. The dip 

 and strike are variable, but generally about east and west magnetic, 

 and the dip is also irregular, but almost always to the southwest, and 

 at almost every angle from nearly horizontal to vertical ; the strike is 

 nearly parallel with the line of the Straits. Near the upper limit of 

 the Cretaceous, are sandstones YQvy like those of Monte Diablo, which 

 accompan3^ the coal, and they contain a considerable quantity' of car 

 bonaceous matter, but no regular coal bed, so far as yet disco\'ered. 



=•'• Geology of California, vol. 1. 



