AGE OF THE NEW IDRIA ORE. 307 



the connection between tliem and the fissures striking northwest-southeast 

 may sometimes be indirect, but is not likely to be entirely wanting. I can 

 see"^ no indication that the mine "is exhausted, and I believe that more 

 bonanzas exist to the south of the clay wall and perhaps also beneath the 

 old group Of stockworks, or on the lower portion of the Elvan Streak vein. 

 ^Age of the deposit.— The cxisteuce of cinnabar in the Washington croppings 

 shows that the deposit is as late as the beginning of the Tertiary period. 

 Tiie deposit also seems to be later than tlie tilting of the Chico beds, 

 which undoubtedly took place at the uplift shown by Professor Whitney to 

 have occurred at the close of the Miocene. The eruption of lavas in the 

 Coast Ranges seems to have begun earl}' in the Pliocene, probably at its 

 commencement. The period of ore deposition at New Idria thus seems to 

 be within the volcanic epoch. It is probably much more recent than the 

 Post-Miocene upheaval. The quantity of cinnabar found in tlie soil was 

 small, tending to jn'ove that no great erosion had taken place since its depo- 

 sition. The ore bodies near the croppings are such as occur most frequently 

 near the surfoce as it existed at the time of ore deposition. This relation 

 will be found enlarged upon in several of the investigations recorded in this 

 volume, particularly that of the Redington mine, where also stockworks 

 and veins are associated. There is nothing at New Idria to suggest a con- 

 siderably greater age than that of the Redington deposit. The latter is cer- 

 tainly Post-Pliocene. 



In a drift near the stockworks on the lower tunnel level I met with 

 what is at least a very curious and suggestive occurrence, which may have a 

 bearing on the age of the deposit. The drift had not been used for years, and 

 the waUs were coated with epsom salts and other secondary minerals to the 

 depth of nearly two inches. In this loose coating I found a tiny seam of 

 cinnabar which had quite beyond question formed in this position since 

 the drift had been abandoned. This proves that mercuric sulphide still 

 exists in solution in the waters of the mine. It may be that the solution 

 from which this little vein was deposited was a remnant of that frOm which 

 the great ore bodies were precipitated. If so, the period of ore deposition 

 is not even yet wholly past. But it is also not impossible that this cinna- 

 bar was leached from the stockworks by surface waters impregnated with 



