810 HISTORICAL GEOLOGY. 



1892). It is probable that there were ranges of flexures and monoclinal 

 shoves along the rest of the Sierra to the southward and great upthrust faults 

 also in the Taylorville region. 



The maximum thickness of the rock in the Taylorville region is 24,500 

 feet, of which 17,500 feet are Paleozoic and 7000 feet Mesozoic (Diller). 

 The Sierra Il^evada geosyncline of depositio:!, which began during or before 

 Upper Silurian time, hence reached in this part a depth nearly of 25,000 

 feet ; this was the thickness of the pile of deposits that was upturned and 

 flexed in the crisis of mountain-making at the close of the Jurassic. The 

 heat generated by the movements was sufiicient for the rather feeble meta- 

 morphism which characterizes the rocks. Facts also appear to prove that 

 the core of diorytic granite, which is the chief rock of the ridge to the south, 

 was an Archaean ridge over and against which the thrust took place ; for the 

 stratified rocks, where in contact with it, show in some places in their 

 crystallization or metamorphism the effects of the friction. For an example 

 of such effects, see page 534. This view of the Archsean age of the Sierra 

 core of granite is presented by King in his 40th Parallel Report, 1878. 



The Sierra Nevada, when first formed, probably had not half its present 

 height. It has a later history of great geological interest. 



The formation of the gold-bearing veins of quartz in the Sierra rocks was 

 a consequence of the upturning. The wrenching of the strata' opened the 

 leaves of the slates, and also made great intersecting fissures. The opened 

 spaces and fissures became filled with silica (quartz) which the heated mois- 

 ture took into solution, and also with such ores as the vapors found in the 

 beds. Some of the auriferous quartz veins have a width of 10 to 40 feet. 

 As the modern Sierra gravels contain gold from the rocks which make the 

 modern Sierra, so the more ancient rocks, of Jurassic and earlier origin, must 

 have held gold from the earlier crystalline rocks of the Sierra; and this gold, 

 with ores of lead, copper, and other metals, the hot vapors gathered into the 

 fissures. It was not the work of superficial waters ; for the veins now visible 

 on the Mariposa estate and elsewhere are, owing to denudation, thousands of 

 feet below the original surface ; but there is no doubt that superficial waters 

 took part in the work. The metamorphic effects include many rocks in the 

 Coast Range, besides prevailing kinds above mentioned, as stated on page 318 ; 

 and through Becker's studies the region has become an especially instructive 

 one on the general subject of metamorphism. 



The "granite core" of the Sierra constitutes the culminating points in the southern 

 portion of the range — among them Mount Wliitney, which has a height of 14,898 feet 

 above sea level ; and it is the rock of the famous Yosemite Valley. Whitney states 

 that the slates near the granite are harder than at a distance from it, and contain horn- 

 blende ; that veins of granite extend into the altered schists. And Diller describes 

 contact phenomena observed by him in the Taylorville region. Moreover, some of the 

 auriferous quartz veins extend into the granite. Evidence of this kind led Whitney, in 

 his California Report, to present the view of the post-Jurassic age of the granite ; and 

 several recent investigators of the region hold the same opinion. But intrusions of 



