Ifesozofc and Cosaozoic Geology and Palaeontology. 11 



31. radiata, M. navis. Area horni. A. gravida^ A. decurtata, Cucvllcea 

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

 opsis transversa, Pecten trasM, P. operculiformis, P. californicus, 

 Lima microtis, L. appressa, Plicatula variata, Ostrea hreweri, Exo- 

 gyra parasitica, Terebratella ohesa.^ Flabellum remondianum, Tro- 

 chosmilia striata, Astroccenia petrosa, Ficus mam^millatus, now Fi- 

 copsis mammillatiis, Natica uvasana, Scalaria matthewsoni, Turri- 

 tella infra-granulata, Chione angulata, now Callista angulata. Tapes 

 cretacea, Cardita veneriformis, Yoldia nasuta, Placunanomia inor- 

 nata; from Siskiyou INIountains of Oregon, Siliqua oregonensis., Tell- 

 ina whitneyi, Dosinia pertenuis, Modiola siskiyouensis, now Volsella 

 sisklyouensis, and Ostrea mallei.formls. 



In 1865, J. D. Whitney* described tlie Contra Costa Hills, whieli 

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

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

 Custa county into Alameda and Santa Clara, and finally become 

 merged in the Mount Hamilton division of the Monte Diablo Range. 

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

 metamorphosed, although a belt extending along their western side is 

 considerably altered from its original character. 



Beginning at the northwest extremity 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 

 forming bands and lenticular masses in the shales, generally but a 

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

 strike is usually 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 layers 

 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 very like those of Monte Diablo, which 

 accompany the coal, and they contain a considerable quantity of car 

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



■^- (ieolpgy of California, vol. 1. 



