Mesozoic and Coinozoic Geology and Paloiontology. 79 



but often gray and green, with reticulations of quartz, like the rocks 

 of Monte Diablo, and consists of metamorphosed Cretaceous rocks. 



North of the mouth of San Luis creek the strata consist of conglom- 

 erates, sandstones and shales of Cretaceous age. The conglomerates 

 generally form the crests of the ridges, and are very coarse, containing 

 numerous boulders from one to two cubic feet in size. These consist 

 of porphyry, granite, and various forms of metamorphic rock, entirely 

 unlike the metamorphic Cretaceous of the center of the chain. ^ 



Thejaspery beds of Chisnantuck are the exact counterpart of those 

 of Monte Diablo, which we know to be Cretaceous, and those of Mine 

 Hill, which contain the deposits of cinnabar, are evidently the continua- 

 tion of those of Mount Chisnantuck. And as we trace them farther 

 north, to the extremity of the peninsula, we find them still retaining 

 the same lithological character, while we have there the evidence of 

 fossils to prove them to belong to the Cretaceous epoch. Deposits of 

 cinnabar have been found in rocks of Triassic and Tertiary age, but 

 the large and valuable deposits are in the Cretaceous. 



The larger portion of the rocks which make up the north end of the 

 peninsula of San Francisco, are Cretaceous. The rocks in the vicinity 

 of Clear Lake, when not of volcanic origin, are Cretaceous, and are the 

 continuation of a great belt of strata of this age, which commences at 

 Benicia, and stretches off to the northwest for an indefinite distance, 

 apparently coming out to the ocean in the neighborhood of Cape Men- 

 docino. The termination of the Coast Range at Benicia is of unal- 

 tered Cretaceous strata, much broken, and forming rounded hills, des- 

 titute of trees. Here as in Contra Costa county', the Cretaceous is well 

 represented both by the bluish clay shales, with interstratified beds of 

 argillaceous limestone, and by the overlying masses of blue and yellow 

 sandstones, the latter in very heavy beds. 



The Cretaceous formation, which is seen cropping out near the 

 northern base of the twin sisters, is continuous from that place as far 

 north as Capel Valley, at which point it becomes metamorphic and 

 broken. The hills lying between the Sacramento and Suisun Valleys 

 are of this age, and appear to form a line of foot hills along a high 

 Cretaceous ridge, made up of unaltered shales and sandstones, running 

 nearl}' northwest and southeast, and extending from Suisun Bay to 

 Puta Creek. This range is about 3,500 feet high, and the ridge along 

 the summit is formed by heavy bedded sandstones. 



Cretaceous strata, in the San Emidio Canon, are seen resting on the 

 granite and upturned edges of the mica and hornblende slates. At the 

 Canada de los Alisos, which debouches into the plain four miles east 



