CALIFORNIA GRANIIE. 175 



ever that the material of which tliey are composed has ever yet been de- 

 posited from water, and, on the contrary, there are weighty reasons for 

 supposing that they have ascended through primeval rocks. The absence 

 of hydrocarbons in a part of volcanic emanations is also, as Bunsen showed, 

 a very strong argument against the supposition that any organic matter (or 

 any sedimentary rocks of later date than the origin of life) exists at the 

 sources of volcanic activity. An argument in favor of tlie sedimentary 

 origin of lavas is often drawn from the supposed great variations in the 

 composition of these rocks. This seems at first sight to be justified by the 

 literature of lithology, but those who have specially occupied themselves 

 with that branch of geology are well aware that the uniformity of eruptive 

 porphyries is astonishing and that typical rocks are tlie rule the world over. 

 In geological reports hundreds of square miles of a normal lava will be 

 described in a paragraph, while a few square yards of some abnormal, 

 highly exceptional variety of the rock will require pages of description and 

 discussion. The literature of the subject is thus apt to convey a false im- 

 pression. 



Conclusions. — The argumeuts presented as to the origin of the massive 

 rocks of Califi)rnia may be briefly summarized. If the mechanism of up- 

 heaval and subsidence is considered, it seems impossible that rocks from 

 beneath the accumulation of clastic material should not often be brought 

 to the surface. If the mechanism of erosion is considered, it appears most 

 improbable that, through degradation in any combination with subsidence, 

 the entire area of primeval rocks should ever disappear for any length of 

 time. The deepest-seated rocks known are granitic. If the conditions 

 attending the earliest precipitation of water on the earth's surface be consid- 

 ered, these conditions seem to be those known experimentally to favor tlie 

 production of crystalline minerals and which are believed on good grounds 

 to be those attending the formation of granite. The evidence in California 

 is all in favor of the hypothesis that the main mass of the underlying granite 

 is primeval, or that it antedates the formation of extensive oceans, and tliat 

 it is free from organic matter. The lavas come from beneath the granite 

 and are, a fortiori, thoroughly Azoic. 



