414 J. E. MILLS — LOCKS OF THE SIERRA NEVADA OF CALIFORNIA. 



Page. 



Mesozoic Rocks outside of upper Feather River District 4:;:: 



Distribution of the Rocks 4:!:! 



Fossiliferous lower Mesozoic Limestones 433 



Eastern principal Area 435 



Ammonites colfaxii 436 



Mesozoic Exposures south of the American 43(5 



Mesozoic Exposures south of the Merced 4.'!7 



The Mesozi tic Series 4.">s 



Natural Divisions 438 



F( issil 1 lorizons 439 



Alteration Products ... . 44(1 



The quartzitic Alteration 440 



Pyritous ( lharacter of the Pocks 440 



Fissures and mineral Veins 440 



Gold 441 



Fissures containing Chalcopyrite 442 



Age of the mineral Veins 443 



Introduction. 



General Character of the Sierra Rocks. — The great muss of the Sierra 

 Nevada consists of crystalline rocks (granites) and highly metamor- 

 phosed, tilted and dislocated sedimentary and eruptive rocks. There 

 are less metamorphosed strata of later age (Cretaceous and Tertiary) on 

 the western Hank at and near the foot of the range, and Tertiary and 

 Quaternary lavas and sediments deposited by streams occur on the 

 slopes and even on crests and peaks, especially of the northern half of 

 the range. But the great mass of the range is made up of granites and 

 of sedimentary and eruptive rocks so highly metamorphosed as to he 

 quite generally designated as the metamorphic rocks of the Sierra. 



J. D. Whitney showed in his report on the geology of California, and 

 added confirmation in his work on the auriferous gravels of the Sierra 

 Nevada, that a portion of these metamorphic rocks are of Mesozoic age, 

 and in the same works he states, with less positiveness, however, that a 

 part of them are of Carboniferous age* The Mesozoic age of the rocks 

 regarded by Whitney as Jurassic is farther confirmed by C. A. White 

 and G. F. Becker, though White assigns them to a position at the con- 

 lines of the Jurassic and Cretaceous periods,f and Becker places them 

 higher up in the Cretaceous;;!; hut the limits of the groups of these rocks 



*()n identification of Mesozoic fossils by W. M. Gabb and F. I'>. Meek, and of Carboniferous 

 fossils found outside of the Sierra proper by J. B. Trask am! fragments of fossils found within the 

 Sierra by W. M. Gabb. 



T Bull. U. S. Geol. Survey, no. 1."., 1885, p. 26. 



; Bull. I'. S. Geol. Survey, no. L9, Ins;,, pp. 9-18; also Bull. Geol. Soc. Am., vol. 'J. 1890, pp. 201-208. 



