Doc. No. 9.] 15 



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primitive rocks occurring, and an outcrop of serpentine makes its ap 

 pearance, together with some of its subordinate members, among which 

 the Shales and some of the cherty rocks appear. These are flanked to 

 the east with rocks of the trapean group, forming the high ridge in that 

 direction, and are surmounted with the fbssiliferous sandstones. The ser 

 pentine rocks of this district contain considerable quantities of chromic 

 iron, but its extent is not accurately known. South of Oakland to San 

 Antonio, the country is of the same character as that immediately pre 

 ceding it. The mountains were not examined, but the creek was fol 

 lowed four or five miles, and its bed showed nothing to indicate a change 

 in the structure of the country from which it has its rise, with the 

 exception, perhaps, that the sandstone pebbles exhibited no marks of 

 fossils. 



These features were general for the entire distance to the San Leandro, 

 being about eight miles : but after crossing this stream, the fossiliferous 

 rocks become more fully developed and continue to gradually increase 

 to the arroyo of the Alameda. The sedimentary rocks of this district 

 rest on the older trap formations, with frequent small threads of quartz 

 passing through them, but no material change of structure was observed 

 in these at the points of contact. The sandstone of these hills is 

 much coarser in its texture than that forming the shores of the Bay 

 San Pablo and Straits Carquinez, and its fossils exceedingly fragile and 

 imperfect. 



Crossing the Alameda and entering the hills in which the Mission of 

 San Jose is situated, a distance of four miles, no change in the general 

 character of the rocks is noticeable, with the exception that the sedimen 

 tary rocks have suffered more from disintegration than at any point 

 north of the arryo Alameda, and the contour of the country being such 

 as to retain a large part of the detritus of these rocks, the result has been 

 the production of a soil, throughout the hilly and rolling districts, of 

 almost unequalled richness and fertility. 



Following the west side of the Central Range we pass into the 

 county Santa Clara, a short distance south of the Mission San Jose. 

 The sedimentary rocks containing fossils continue to cap the summit of 

 the ridge for the distance of twenty -five miles south of this point, all 

 of which appear to be of the same age as those above described. South 

 of the Hot Springs (a point defining the boundary between the counties 

 Alameda and Santa Clara) the trachytes, crop out in two or three locali 

 ties, leaving but little room for doubt that the more recent of the volcanic 

 rocks underlie this entire section. At the distance of sixteen miles south 

 of the Spring, the chlorite slate flanks the west base of the ridge, and at 

 short intervals along this distance fragments of these rocks are frequently 

 met ; on the Rancho del Palo this rock again occurs at a distance of three 

 miles east of San Jose, here it crops out on the hills three hundred feet 

 above the valley, and appears to have been much disturbed and broken 

 up ; immediately west of this an alluminous slate appears dipping south 

 west and corresponding to the inclination of the chlorites. 



In the hills of this district there is considerable quantities of quartz, 

 some of which has proved auriferous. 



Traveling parallel with the ridge and south of the Pueblo San Jose, 

 the fossiliferous rocks become less developed, and at the distance of 



