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University of California Publications in Geology [Vol. 13 



feet from the diabase margins in the Cobalt Series of sediments. Even 

 the noncommercial deposits and traces of cobalt in the northern part 

 of the province are clearly related to the diabase, and no occurrencee 

 are known in this whole region that are clearly related to deep fissures 

 in controversion of this rule. These facts are taken as strong evidence 

 that the visible diabase itself was the source of the ores. 



Negation was resorted to in order to exclude any supposition that 

 the ores might have originated either through the downward circula- 

 tion of vadose waters or through the upward circulation of juvenile 

 or of hot meteoric waters. These matters need not, perhaps, be re- 

 viewed here further than to recall that the principal points made in 

 regard to ascending solutions were : ( 1 ) that the heated mineral waters 

 of the earth, whatever their origin, are known to be very dilute, so 

 that large volumes would be recuiired to pass through the rock in 

 order to produce a moderate amount of metasomatic ore; (2) that in 

 the absence of crustification and comb structure, metasomatic veins 

 can be supposed to have grown only by marginal accretion; (3) that 

 the chief circulation of underground water must be through fissures, 

 and that its passage in volume through pore spaces must be practically 

 inhibited by the large coefficient of friction due to the narrowness of 

 the capillary and subcapillary openings and the tortuousness of its 

 course; and (4) that, at least in the case of the silver ores under dis- 

 cussion, the veins and vein walls offer no more porous courses for the 

 passage of water than the country rock offers, and therefore there 

 would be no directive agency to cause mineral-bearing solutions to 

 circulate there rather than at random through the country rock. 



At Cobalt the chief ore production has come from beneath the 

 diabase sheet, the veins being metasomatic replacements of the walls 

 of cul de sac fractures. It seems far-fetched to suppose, since the 

 diabase invaded chloritic schists which must have been saturated with 

 ground water, that mineral-bearing solutions could have circulated 

 downward from the diabase into the already saturated country rock 

 in sufficient quantity and strength to have produced such metasomatic 

 deposits in those blind fractures. Local convection currents could 

 be supposed to have only gone round and round in a fracture of 

 that sort without any chance of replenishing their original supply 

 of mineral. 



AVater circulation being practically inhibited, recourse must be 

 had to the principle of diffusion to explain the transference and depo- 

 sition of mineral ; but slow as would be the migration of metalliferous 



