470 QUICKSILVER DEPOSITS OF THE PACIFIC SLOPE. 



The Great Western lies near the extinct andeaitic volcano called Mt. 

 St. Helena. The country rock "is of the metamorphic series, and both ande- 

 site and basalt have broken tln-ough it. A layer of o|)alized serpentine 

 accompanies the ore-bearing ground. The ore is chiefly cinnabar, but at 

 one point rock impregnated with native mercur\- was found. The cinnabar 

 was deposited simultaneously with pyrite and quartz. The bitumen posep- 

 nyte was first described from this mine. The deposit consists of a tabular, 

 reticulated ma.ss connected with a fissure system and it lies at the contact 

 between serpentine and nearly unaltered sandstone. If it does not come 

 under tlie common definition of a vein, it is closely related to that class of ore 

 bodies. 



The Great Eastern lies in Sonoma County, far from other quicksilver 

 deposits and six miles from lava. The rock is the ordinary metamorphosed 

 material of the Coast Ranges The ore occurs in black, opalized serpentine, 

 which here forms a definite ledge. The ore seems, as usual, to be of some- 

 what later date than the formation of opal and is accompanied by pyrite, 

 quartz, and bitumen. The ore seems to form a pipe, which is continuous 

 from tlie surface to a depth of 450 feet. This pipe I believe to lie on a 

 continuous fissure. 



All of the above mines have produced important quantities of quick- 

 silver. 



Other quicksilver deposits. — So far as I kuow, tlic uiost northerly cinnabar 

 deposits on the west coast south of British Columbia are in Douglas County, 

 Oregon. In the northern part of Trinity County, California, there is also a 

 mine. These widely separated deposits both lie on the northerly continua- 

 tion of the middle Coast Ranges, where most of the deposits occur. From 

 Clear Lake to Santa Barbara, as is shown on the map of California accom- 

 panying this report, the deposits are thickly scattered. 



Of the very many deposits briefly described in Chapter XIII, onh- a 

 few can be mentioned liere. The Manzanita mine, Colusa County, is very 

 remarkable for the association with cinnabar of free gold, often in feathery 

 crystals. Pyrite accompanies the ore and the gangue is chiefly quartz. There 

 is free sulphur also, as well as other evidence that the ore was deposited 

 by hot sulphur springs, such as still issue within a few hundred feet of the 



