362 QUICKSILVER DEPOSITS OF THE PACIFIC SLOPE. 



This mineral is doubtless posepnyle, although many of its phjsical 

 characteristics are not altogether like those ascribed to that mineral. 



The deposit of the Great Western appeared to be a tabular, reticulated 

 mass, connected with a fissure system. It was certainly precipitated from 

 solutions, and these wei'e probably dependent upon volcanic action which 

 attended the eruption of the adjacent lavas. No hot waters or gases, how- 

 ever, now enter the mine. 



THE GRE.\T EASTERN. 



Importance and position. — Tliis miuc is iu Sououia Couutv, about three miles 

 north of Guerneville. There is another mine of the same name in Lake 

 County, near the Great Western, which will be referred to in the next 

 chapter. The Great Eastern of Sonoma County has a considerable eco- 

 nomic importance, having yielded over eleven thousand flasks of metal and 

 having been able to continue pi-oduction in spite of tlie great depression in 

 the price of quicksilver during the past few years. The Mt. Jackson mine, 

 which is on the same ledge as the Great Eastern, has also produced .597 

 flasks, but has not been worked of late years. Tlie deposit upon which 

 these two mines are situated is somewhat remarkable for its isolation. 

 Not only is it above twenty miles from the nearest quicksilver mine, but 

 it lies away from the course of any line of deposits. It is also somewhat 

 distant from manifestations of volcanic activity, the nearest known lavas 

 being about six miles east of the Great Eastern. 



General geology. — Tlic distHct survcycd prcscuts little interest from the 

 point of view of general geology. The surface is exclusively occupied by 

 the series of irregularly metamoi-phosed rocks so prevalent in the Coast 

 Ranges. Slightly altered sandstones and shales, impure limestones, gran- 

 idar metamorphics, schists carrying glaucophane and garnet, phthanites, 

 and serpentine are all represented. So thoroughly mingled are these vari- 

 ous substances, however, and so numerous are the transitions that it would 

 be entirely impracticable to represent the varieties by colors on the map 

 (Plate VII). 



Although a portion of the beds are so little altered that fossils might have 

 been tolerably preserved in them, no organic remains could be detected. 



