334 RESOURCES OF CALIFORNIA. 



CHAPTER X. 



GEOLOGY. 



259. Plutonic and Secondary. The rocks of California 

 are mainly Plutonic, upper Secondary, Tertiary, and Volcanic. 

 The Plutonic, or granite, forms the bulk of the Sierra Nevada 

 and part of the coast mountains. The upper Secondary occu- 

 pies a belt on the western slope of the Sierra Nevada, vary- 

 ing from five miles in width, about latitude 35, to forty 

 miles in latitude 39. Its lower edge is in places within five 

 hundred feet of the level of the sea ; its upper line 6,000 feet, 

 but the average elevations of the two edges are probably 

 1,000 and 4,000 feet. The rocks of this formation are 

 mainly slates, and in them are found the seams of auriferous 

 quartz and the deposits of gold-bearing gravel which first at- 

 tracted a large population to California. These slates are 

 found, also, in the northern coast mountains ; and in the 

 Sierra Nevada a belt of limestone is associated with them. 

 In the coast mountains, south of 39, and also in spots on the 

 Sierra, cretaceous rock, the highest of the secondary forma- 

 tion, appears, and it is accompanied by coal and quicksilver. 



260. Tertiary. The Tertiary formation, stratified and 

 metamorphic sandstones, occupy the valleys in the middle 

 and southern portions of the State, the greater part of the 

 coast mountains, and the lower foothills at the back of the 

 Sierra Nevada. The strata on the coast mountains have been 



