18 



than in many parts of the more northern equivalents of this part of the chain, 

 or more particularly such as may be found in the Santa Cruz and Monte Diablo 

 ranges. 



The Serpentine rocks of the country included in the southern branches of the 

 Nacistniento River support in several localities heavy beds of the Miocene sand 

 stones, the fossils of which agree in all particulars with those'noted as occurring 

 in the same group of rocks throughout this part of the State. On the northern 

 extremity of the talcose series, a vein of quartz has cut through the inferior 

 rocks, and also through the sedimentary group, resting upon them; among the 

 sandstones it has sent out several lateral veins, and the points of contact exhibit 

 very marked changes in structure, equally distinguishable with any of those 

 cases noticed in former reports, where the contact of lavas were observed on an 

 extensive scale. 



Nor are the changes of structure confined to the intrusion of the latter veins 

 alone, for in following out the igneous intrusions, it was found that considerable 

 dikes of the trapean rocks were manifest, the effects of which were apparent 

 both'by change of position and structure, the latter to an eminent degree. An 

 other illustration of the effects of those late trapean intrusions is most clearly 

 marked in the case of the Los Angeles sandstone about one mile north of the 

 town, where the latter beds containing impressions of marine plants and other 

 fossils have been most completely metamorphosed, so much so was this the case 

 that the rocks would fracture transversely to the lines of stratification with as 

 much ease as in any other direction. The fracture was usually conchoidal with 

 sharp, well defined edges, and the fragments had a distinct sonorous sound. 



Leaving San Inez and passing in a southeast direction to the San Fernando 

 Mountains, we find a continuation of the primitive groups which are apparently 

 connected with and continuous into the coast mountains to the north; they are 

 met with in the Cafiada Los Ubas, and are continuous from thence into the 

 coa^t mountains to the west, and the southern terminus of the Sierra Nevada. 



The rocks in the vicinity of the Tejon are granitic, consisting of Sienite, Horn 

 blende Graitfje, a goodly amount of the more felspathic rocks, containing im 

 bedded crystals of hornblende and schorl, with Mica and hornblende schists. 

 They evidently belong to one and the same group, having an age contemporane 

 ous with that series found some two hundred miles farther to the north. 

 South of the terminus of the Sierra Nevada, and on the western edge at 

 the desert, are to be found small masses of scoria with small fragments of 

 Obsidian, the latter riot abundant. 



The above general characteristics are sufficient to fix the relative ages of 

 these distant groups, of allied rocks, and when we remember that nearly 

 throughout the entire range of the mountains they traverse, that another and 

 widely distinct formation is found reposing upon them, the features of which 

 either at its extremes or centre are congenerous in character, or but slightly va 

 riant. The great uniformity thus manifested in the primitive rocks below, and 

 the sedimentary group above leads us most irresistibly to the conclusion that 

 cotemporaneous origin in each is most distinctly marked. 



It must not be inferred from the above that more recent disturbances in these 

 districts have not taken place, for this fact has been before noticed in former 

 reports while speaking of other parts of this range, and the same is also observ 

 able in the district under consideration. The principal differences in fossilifer- 

 ons character among the superior sedimentary deposits of this particular pe 

 riod will be found attributable more to climatal influences, rather than to any 

 apparent differences in relative age; for latitude exerts a much less influence on 

 species than temperature. 



The differences in species found at the extremes of this group of sedimentary 



