582 THE JOURNAL OF GEOLOGY. 



bearing upon the phenomena here discussed is likely to be found 

 in that region. 



In southern Oregon,, on the line of the Southern Pacific Rail- 

 way, the writer has on several occasions observed the eruptive 

 contact of an extensive granite mass against sedimentary strata 

 which have been mapped as "Auriferous slates," which are prob- 

 ably early Mesozoic or Carboniferous in age. The intrusion of 

 the granite into the sedimentary rocks is unquestionable, the 

 relations being well exhibited in the excellent exposures afforded 

 by the railway cuttings. 



In California the statements of Whitney 1 and the more recent 

 writings of the geologists of the U. S. Geological Survey, Diller, 

 Becker, Turner, and Lindgren, and of Mr. H. W. Fairbanks, 

 seem to leave no room for doubt that a great part, probably the 

 greater part, of the granitoid rocks of the Sierra Nevada is of 

 Mesozoic age, and has invaded the now more or less altered sedi- 

 mentary and volcanic rocks known as the "Auriferous slates," 

 which range in age from the Silurian up to the Jurassic. 



Here again we have clearly to deal with a granitic batholite 

 which must, by absorption or otherwise, have replaced a large 

 portion of the preexisting lower rocks in the region affected. 

 From the facts recorded by able and critical observers, this 

 conclusion holds, notwithstanding the probability that there may 

 also be remnants of an older granite to be discriminated from 

 the Mesozoic mass. In the southern Sierra, as Becker has, with 

 wise caution, pointed out, we approach the region of Archaean 

 granite known in the Grand Canon section. It would therefore 

 be not at all remarkable to find these more ancient granites 

 involved with the newer in the Sierra Nevada. But their presence 

 could not affect the important fact of an invasion of the crust 

 during middle Mesozoic time by an immense granitic batholite, 

 which invasion without doubt had much to do with the meta- 

 morphism of the strata which survived the upward progress of 

 the magma into the crust. 



Here again the development of the batholite seems to have 

 1 Geology of California, Vol. I. Auriferous Gravels. 



