Park. — Origin of Metal- bearing Solutions. 105 



1. The lateral-secretion theory supposes — 



(a.) That the filling of cavities was the work of descending 



meteoric waters ; 

 (6.) That the filling-matter was principally obtained from 



the adjacent rocks by a process of leaching by thermal 



waters. 



2. The ascension theory assumes — 



(a.) That the filling of veins was effected by deep-circulating 

 waters, ascending through open or partially open 

 fissures ; 



{h.) That the mineral and metallic contents were derived 

 from a deep-seated mineralised zone. 



Many writers assume that ascending and descending waters 

 are merely units in what may be termed a hydraulic circuit, 

 the interchange being caused by gravitation assisted by capillary, 

 and the dift'erence of temperature of the ascending and descend- 

 ing waters. Much of the movement, it is claimed, is necessarily 

 lateral and towards channels filled with ascending waters. 



It was maintained by Professor Posepny and Dr. Raymond 

 that descending waters were merely oxidizing, and incapable of 

 depositing sulphides. This contention has, however, been suc- 

 cessfully disproved by Emmons, Becker, Van Hise, and othc-r 

 American geologists, who have shown the existence of secondary 

 sulphides both above and below water-level, or in what may be 

 termed the zone of vadose circulation. 



Professor Daubree always maintained that metallic sulphides 

 could not be deposited without the agency of organic matter ; 

 but Skey, as far back as 1870, proved experimentally that 

 from its solution of carbonate of soda, potash, and ammonia, 

 gold is reduced by sulphides, but not from its solutions in alka- 

 line sulphides.* He found that 1 grain of iron-p>Tites was 

 able to reduce 8'5 grains of gold. 



W. Skey, Trans. N.Z. Inst., Vol. iii, 1870, p. 226. 



