SIMILARITY OF THE DEPOSITS. 405 



ceeding chapters other groiuuls will l)e stated for attributing all of them to 

 this cause. 



Partial absence of sinters. — Eveii if tlio orcs of tlie Kedingtou, Ne.\v Alniaden, 

 and New Idria mines were not deposited from hot springs, like those of Sul- 

 phur Bank, the structure, as will be seen below, would lead to the conclusion 

 that their present cropping-s were not far distant from the surface of the conn- 

 try at the time of their formation. No spring deposits, however, were found 

 at the croppings, and the dissemination of cinnabar in the superficial soil at 

 the first two localities shows that a certain amount of erosion has taken place. 

 In this connection it is worth observing that the springs of Sulphur Bank 

 have made practically no accumulation of material at the surface. Thev 

 have indeed deposited sulphur, but thev have also e.xtracted a large amount 

 of material from the basalt. Perhaps this is due to the sulphuric acid formed 

 by oxidation of the hydrogen sulphide. This acid must convert the car- 

 bonates into soluble sulphates and precipitate the silica as particles which 

 are carried off in suspension. Were the water to cease flowing and erosion 

 to supervene, the disintegrated basalt and the sulphur overlying the ciinia- 

 bar would quickly be swept away and no trace of surface action would be 

 left. At Steamboat Springs, also, it is remarkable that, where the cinnabar 

 is known to be tolerably abundant, there is no superficial layer of sinter. 

 On the contrary, a bnsin has formed, seeming]}^ by the collapse of the dis- 

 integrated granite. The deposits of calcareous and siliceous sinter are asso- 

 ciated with the more recent springs, which carry but little (piicksilver and 

 do not form enough sulphuric acid to remove the lime. The lack of super- 

 ficial sinters and native sulphur at New Almaden and other mines is there- 

 fore no indication that they were not deposited from hot .springs. 



Evidence from the mode of occurrence. — If the scHes of fjuicksilver deposits the 

 genesis of which is discussed in the foregoing pages be considered from the 

 point of view of the form and structure of the ore bodies, nothing incon- 

 sistent with asserted community of origin will be found ; on the contrary, 

 they form as perfect a series of transitions from a geometrical as from a 

 chemical standpoint. That a close connection exists between the deposition 

 of gold and that of quicksilver is certain, and it is more than probable that 

 other ores sometimes form in large quantities under similar conditions; but 



