SUJIMAllY. 453 



la3'as. The other coincides with the western ranges of the Cordillera system 

 of America. In man}' parts of the world volcanic phenomena are intimately 

 associated with these axes of disturbance and with tlie quicksilver deposits. 



The minerals which occur in consIderal)le quantities with quicksilver 

 ores are few in numlier. Pyrite or marcasite is nearly or quite always 

 present, arsenic and antimony are found at many localities, and copper 

 ores sometimes accompany cinnabar. Other metalliferous minerals are 

 comparatively rare. The })rincipal gangne seems to be invariably either 

 silica, sometimes livdrous, or carbonates, chietly calcite. Cinnabar occurs 

 in true, simple fissure veins, in impregnations, and stockworks. The forms 

 which its deposits take do not apparently differ in any essential respect 

 from those whicli deposits of other metals assume ; but ore liodies precipi- 

 tated by substitution do not appear from the descriptions to be conmion. 

 In all cases a fissure system seems probably associated with the deposits. 



The facts recorded point to the supposition that most of the quicksilver 

 deposits, if not all of tliem, have been formed in a similar manner. They 

 have all been deposited from .solution, for the gangue minerals could have 

 been formed in no other way. Cinnabar has certainly Ijeen deposited by 

 thermal springs of very high temperature at Puzzuoli, in Italy, and at Lake 

 Omapere, in New Zealand, and is most intimately associated with hot 

 springs and other volcanic phenomena at a large number of other points. 

 It has, perhaps, always been deposited by heated waters. It must l)e 

 derived from some deep-seated substance of world-wide distribution, which 

 has been expo.sed to the action of volcanic solvents by profound disturb- 

 ance. The fundamental granitoid i-ocks answer this descri[)tion, for they 

 seem everywhere to underlie all other rocks ; they are of great but unknown 

 thickness, and they certainly in part overlie the centers of volcanic activity. 

 Geological investigations have as yet revealed no other substance of similar 

 distribution. There is no other rock from which it is equally probal)le tliat 

 the quicksilver is derived. 



The sedimrntary rocks. — Exccptiug tlic light crcaui-colorcd scliists of i\Iioceiie 

 age, which occupy a narrow strip along the coast of California from the 

 neighborhood of Santa Cruz southward, the rocks of the Coast Ranges 

 where unaltered are mainly sandstones of Cretaceous and Tertiary age. 



