19 



rocks, are not more marked than are the present living Mollusca now inhabiting 

 the waters of the coast at corresponding points to the west of any portion of 

 the range. At Point Conception we may find some few of the species that are 

 abundant on other parts of the coast north of this locality, but as a general 

 rule it will be found that the large majority of all the species thus met with will 

 differ very widely from those, even one hundred miles farther to the west, and 

 even at less distances. The same rule will apply to the fossil organic remains 

 of this section of the State, and with much more strictness, as we find the evi- 

 idences of an inland sea, whose natural boundaries were such that a higher tem 

 perature must have existed than ever that which is so characteristic on the 

 south flank of the San Bernardino Mountains at the present time. 



The topography of the country investing its shores was mountainous, and the 

 hills of sufficient altitude to protect it from the harsh winds of the north; an aug 

 mentation of temperature was the natural result producing different organ 

 isms from those at the base of their western declivities; it is thus that we find 

 in the fossil forms of those districts the species that now exist only in the lower 

 latitudes, and which are marked by the Murex, Typhis, Area and Cucullea. 

 On these premises are we able to reconcile some of the apparent discrepancies 

 which have arisen, and place the deposits in their proper geological position as 

 regards the periods at which any portion of this group had their origin, and it 

 explains one of those causes of diversity in species among beds evidently co- 

 temporaneous. 



We have very conclusive evidence before us in this State, that the climatal 

 conditions prevailing during the period in which the Miocene beds were forming 

 was much greater than that prevailing at present, and confined to particular 

 districts, though extending over considerable areas; this arose evidently 

 from the causes above noted. That the shores of the Miocene sea were primi 

 tive is proved from the fact that these rocks are imposed directly on the latter, 

 thus demonstrating that its relative age with that of the northern and eastern 

 chain is widely different and far more recent. 



Since the period of their deposition other and important changes have taken 

 place, and upon the coast line we find the superior beds of . the Tertiary 

 epoch elevated in regular succession above the element in which they originated. 

 How far into the southern interior of the State these groups may extend is yet 

 in an uncertain state, the reports to the present session of Congress from ex 

 plorations of these districts will probably determine this point. 



VOLCANIC ROCKS OF THE COAST MOUNTAINS. 



We come now to the consideration of another and different group of rocks, 

 found in connection with the primitive rocks of this district. Their appearance 

 among the latter demands some consideration, as it is to this group that we 

 must look for many of the mutations observable in this part of the State, as 

 causes producing them were undoubtedly instrumental in producing those mani 

 fest changes so frequently observed among the sedimentary rocks of these moun 

 tains. The volcanic rocks of this part of the coast mountains consist for the 

 most part of intrusions of a scoriaceous and vesicular lava, at other times it be 

 comes much more compact in form, and again exhibiting itself in the form of a 

 light volcanic froth, its colors are various, passing through all the different shades 

 from a yellowish white to a dark iron-brown and black with a semi-metallic lus 

 tre. From what opportunities occurred for their investigation I think there can 

 be but little doubt that their intrusion took place, for the most part, duriug the 

 miocene period, as they appear to have disturbed this group much more seiisi- 



