152 



University of California. 



[Vol. 2. 



SUMMARY AND CONCLUSION. 



The additions made to our former knowledge of west coast 

 geology by the present study are not great. Aside from the 

 contribution to areal geology they are mainly of the nature of 

 suggestions. An effort has been made to confirm as far as possible 

 by facts gathered in this field, what appear to be correct conclu- 

 sions reached by studies of other portions of the coast. Diverse 

 conclusions have been reached concerning certain problems here 

 met with, and in so far as the facts observed in this field bear upon 

 them they have been given their due weight. 



Granite. — The petrographical characters of the granite of the 

 peninsula harmonize essentially with most that is met with in the 

 Coast Ranges southward and with them it forms a more or less 

 satisfactory unit. It differs from the rocks of the Sierra Nevada 

 that have been termed granodiorite both mineralogically and, as 

 far as can be told, chemically. It has its nearest allies in granites 

 of the Klamath Mountains which have not yet been formally 

 described. The age is uncertain but it is, perhaps, contempora- 

 neous with some of the granites, both in the Sierra Nevada and 

 in the Klamath Mountains. If so, it is probably of an age younger 

 than the Mariposa Beds of the Jurassic and earlier than the 

 deposition of the Franciscan (Golden Gate) series. 



Ancient Crust. — The rocks of the pre-granite crust so far 

 as they can be found form a series of limestone, quartzite and 

 a highly metamorphosed crystalline schist. Their physical and 

 petrographical constants, as far as they can be learned, ally these 

 rocks to the Paleozoic, and there is an analogy between them and 

 certain phases of the Devonian rocks of northern California. 



Miocene. — Of the later formations only the Miocene has furnished 

 evidence of any important bearing upon lithology. Certain 

 occurrences upon the peninsula are interpreted to confirm the 

 organic origin of the bituminous shales, as was suggested by 

 earlier writers and more recently advocated by Fairbanks. The 

 highly siliceous character of the shales is thus accounted for while 

 at the same time the structureless and amorphous condition 

 of the silica described by both Lawson and Fairbanks is readily 



