64. THE GEOLOGIST. 



difficnlty, as Dr. Genth truly says, " presents itself on inquiring into 

 the nature of the solvent." The doctor believes the noble metal was 

 dissolved as terchloride of gold :— " If we remember that the decom- 

 position of pyrites produces sulphuric acid, which, in the presence of 

 the never wanting chloride of sodium and a higher oxide of manga- 

 nese, may hberate small quantities of chlorine, the most powerful 

 solvent of gold, we have at least a very plausible explanation." 



Dr. Genth's doctrine is that the gold both of veins and alluvial de- 

 posits is derived from the adjoining rocks, where it exists probably 

 in a highly disseminated state ; from these rocks it is removed in a 

 state of solution, and precipitated in concentrated deposits in the 

 veins and among the alluvial debris. The rock in which the metal 

 most frequently occurs is diorite or greenstone [composed of ortho- 

 clase felspar and hornblende]. How it originally came into this 

 rock is not a question entered upon ; the main point being to prove 

 that the gold of alluvial deposits is not derived, as is usually sup- 

 posed, from the destruction of pre-existing quartz -veins, the fact 

 being that they are both equally derivative, the original source being 

 the neighbouring rock. 



There are many considerations suggested by the mode of occurrence 

 of gold which weigh strongly in favour of such a suggestion. In the 

 first place, gold is continually found in alluvial deposits, in consider- 

 able sized nuggets, in districts where no veins are found. In this 

 case the usual theory is that the original upper surfaces, which were 

 rich in auriferous veins, have been removed by denudation, and that 

 the alluvial gold is the remnant of these. But this has the disad- 

 vantage of assuming an hypothesis, for which no good reason can be 

 given, that there is some peculiar law which limits the orig-inal pro- 

 duction of gold to the surface, and which is held, with a strange in- 

 consistency, by the same men who folly recognize the more than 

 probability of other metals being derived from beneath. Assuming 

 that the gold is derived from the rock by solution, and that the veins 

 arc mere depositories, we have at once at least a plausible reason for 

 tlie general occurrence of gold only near the surface. It is that the 

 solvent of that metal is somehow or other essentially connected with 

 the atmosphere ; so that although gold may exist at all depths, 

 scattered, highly disseminated tlumigh certain igneous rocks, it is 



