76 HAROLD W. FAIRBANKS 



It does not seem to me that there is any validity whatever in 

 the above reasoning, and in the light of the true position of the 

 Golden Gate series there is a strong presumption in favor of an 

 opinion exactly opposite to that just quoted. In fact the pre- 

 sumption is so strong that it amounts almost to a certainty that 

 the granite in the Coast Ranges is older than the main body of 

 the granite in the Sierras. What we at present know of the 

 position of the Golden Gate series points to the fact that its first 

 upheaval was contemporaneous with the last great upheaval 

 recorded in the rocks of both the Sierras and Klamath Moun- 

 tains. The Mariposa beds involved in this upheaval in the 

 Sierras are held to be Upper Jurassic. The Knoxville beds 

 deposited after this upheaval are believed on the best authority 

 to be Lower Cretaceous ; and if we make the granite in the Coast 

 Ranges the same age as that in the Sierras, we must crowd into 

 the break between the Mariposa beds and the Knoxville, a series 

 of beds thousands of feet in thickness and separated from the 

 Knoxville by a break as profound as that between the Knoxville 

 and the Jurassic. 



There is every reason for assuming that the granitic rocks of 

 California are not all of the same age. Granitic bowlders occur 

 in the Mariposa beds south of Colfax, a fact pointing to a pre- 

 Jurassic granite body in that region. 



The youngest fossiliferous rocks associated with granite in 

 southern California are probably of Carboniferous age, and while 

 the extension of the crystalline basement rocks of that region 

 northwestward into the Coast Ranges is not likely to be much 

 younger than the Carboniferous, for all that we know at present 

 it may be much older. 



Harold W. Fairbanks. 

 Berkeley, California. 



