338 KRAMM— SERPENTINES OF THE CENTRAL [June 6, 



serpentine itself, but is most common on contacts with the sur- 

 rounding country rock, shale or sandstone. 



The quicksilver is found filling existing pores, cracks and fissures 

 of this rock. A few cases are known in which the ore is found in 

 sandstone, which however is always in close proximity of serpentine 

 bodies. 



The principal ore is cinnabar. ^Mercury in a free state, meta- 

 cinnabarite, and calomel are of less importance. The most common 

 associates are marcasite, pyrite and chalcopyrite. 



Under high temperature and pressure, in the presence of sulpho- 

 hydrates and carbonates of the alkalies, mercury is in solution as 

 the soluble salt HgS-l-4Na2S. Release of pressure, cooling espe- 

 cially in the presence of ammonia, dilution of the mineral-bearing 

 solution, excess of hydrogen sulphide and the presence of bituminous 

 substances are all factors which enter into the precipitation of the 

 ore, bituminous matter leading towards a total reduction. 



The intrusion of the peridotite masses in shattering the country 

 rock provided channels through which the mineral-bearing waters 

 circulated. These waters not only deposited the ore, but it is 

 reasonable to suppose, that they were also to some extent instru- 

 mental in the decomposition of the serpentine. That conditions in 

 this cherty decomposition product were exceptionally favorable for 

 the deposition of the ore is substantiated by the fact that to the 

 writer's knowledge cinnabar has never been found in the serpentine 

 itself, nor is it found to any extent in the country rock. The few 

 cases known in which the ore is found in sandstone show the sand- 

 stone to be of porous nature and as has been said located in the 

 neighborhood of serpentine dikes. 



As to the source of the quicksilver. Dr. Becker^'^ suggests the 

 base granite which underlies all sedimentary rocks in the Coast 

 ranges. 



Mineralogy of the Serpentines. 



Primary Minerals. 

 The primary rock, as has been shown, with the exception of len- 

 ticular bodies of pyroxenites, is badly altered. Primary minerals 



" G. F. Becker, " Quicksilver Deposits of the Pacific Coast," Monograph 

 XIIL, U. S. G. S., 449, Washington, i888. 



