466 QUICKSILVKR DEPOSITS OF THK TAOIFIC SLOPE. 



ville series. No fossils are known to oc(_-ur in it here, but at tlie northern 

 end of the range they are abundant, and they are found again at San Luis 

 Obispo, to tlie south, in precisely similar rocks. 



On the northeastern flank of the range lie the rocks of the Chico-Ttjon 

 series. These are tilted at angles averaging about 45°, but are only slightly 

 flexed. The loAver part of the series lies unconformably upon the nieta- 

 niorphic beds, as is proved by the structure and by the presence of nieta- 

 niorphic pebbles in Chico conglomerates. 



The Chico and Tejon are absolutely conformable at New Idria and 

 sedimentation went on continuously from one period to the other. Fossils 

 are not numerous, but are present in sufficient number fully to identify the 

 age of the rocks. ]3oth portions of the series show many of the concre- 

 tions mentioned above as due to induration by decomposing organic matter. 

 The T(^jon beds contain coal seams which were exploited on a small scale 

 for many 3- ears. 



No lava exists in the district, but there is a considerable area of basalt 

 just north of Vallecitos Canon, about ten miles from the mine. There are 

 cold sulphur springs, but no hot ones. 



Next to the New Almaden, the New Idria has been much the most pro- 

 ductive cpiicksilver mine in North America. The ore contains the usual 

 mixture of cinnabar, pyrite, and quartz, accompanied by some bitumen ; 

 metacinnabarite also was found in the New Hope lode in very large quan- 

 tities and in less abundance at another point in the mine. The structure is 

 extremely complex, but typically developed stockworks, veins, and imi)reg- 

 nations all occur. Faults and cross-courses make successful explorations 

 very difficult and uncertain. 



The ore is almost entirely deposited in Neocomian rocks, but to a small 

 extent also in the Chico beds. The deposition has taken place since the 

 Post-Miocene upheaval and is seemingly referable to about the same period 

 as the other deposits. Tlie analogies point to the action of hot springs, but 

 there is no direct proof that the solutions were of high temperature. 



The 8aii Carlos, Aurora, Picacho, and other mines which liave yielded 

 small quantities of ore lie at no great distance. In all of them the ore has 

 been deposited in shattered rock masses of the metaniorphie series. No- 



