202 



KNOWLEDGE. 



[Septembeb 1, 1894. 



primarily accompanying the deposition of tlie gold. Of 

 the entire list, however, there was not a single one that is 

 not well known to be i^roducible by deposition from 

 solution, whilst the true volcanic series are conspicuously 

 absent. After all, however, the soundest argument on 

 this point is from analogy, and if there were no other 

 evidence forthcoming, it would yet be safe to conclude 

 that gold, like the other constituents of mineral veins, has 

 found its way into them in solution. When we find 

 crystaUine particles of gold in the midst of a vein filled 

 with crystalline quartz, which we know to have been 

 deposited from solution and not injected in a state of 

 fusion, the inevitable conclusion is that the gold, too, was 

 precipitated from solution, and probably even from the 

 same solution as that which held the quartz dissolved. 

 It is therefore satisfactory to be able to confirm Prof. 

 Lobley's views as to the non-igneous origin of gold by 

 means of a totally different line of argument. 



With respect, however, to Prof. Lobley's next step, in 

 which the ocean is looked upon as the source of this gold, 

 the proposition becomes far more open to debate ; which- 

 ever view we now take, there are difficulties on every side, 

 and the problem assumes such a degree of complexity 

 that its complete solution in the present state of our 

 knowledge is out of the question. It is just possible to 

 suppose that sea water could find its way directly into 

 fissures of the eartli's crust ; nevertheless, direct deposition 

 of the gold from its solution in sea water is pretty well 

 out of the question. In the first place, it is rather difficult 

 to conceive of any system of circulation by which sea water 

 should directly find its way into fissures that were being 

 at the same time filled with a deposit of silica from other 

 sources. Quite apart from the scientific interest of the 

 question, the practical conclusions that would follow from 

 the acceptance of this theory are so far-reaching that they 

 cannot be assented to without the strongest possible 

 proofs. It is fairly clear that if the gold of mineral veins 

 were derived directly from the sea — that is to say, if the 

 descensionists' theory in this form is the correct one — the 

 upper parts of gold veins would be the richest. It is 

 quite true that there is frequently a superficial enrichment 

 of auriferous veins near the surface, due to combined 

 physical and chemical causes, to the concentration, in this 

 portion of the reefs, of the gold derived from the degradation 

 in time past of stiU higher-lying portions now denuded 

 away, such degradation having, of course, occurred 

 subsequently to the consolidation and upheaval of the 

 vein, together with the surrounding strata. It is also 

 true that the upper portions of reefs are mostly richer in 

 free gold than the lower-seated portions, but this again is 

 only due to the oxidation by atmospheric agencies of the 

 previously existing pyrites with which the gold was 

 intimately combined. The total tenour of gold in the vein 

 is not necessarily affected by this latter change, and upon 

 the whole there is no evidence whatever that gold 

 veins become progressively poorer as we go down deeper 

 upon them. Practical gold miners are fond of saying that 

 gold reefs improve in depth, but practical gold miners are 

 a sanguine race, and it seems but too probable that in the 

 majority of cases it is the "wish that is father to the 

 thought." Instances can, no doubt, be quoted where gold 

 mines, like other mines, have improved in depth, but this 

 must by no means be interpreted into a general law. The 

 richness of gold reefs varies in their vertical as it does in 

 their horizontal extension, but not regularly ; in the 

 present state of our knowledge it would be unsafe to 

 predicate more. 



According to Prof. Lobley's view, however, sea water is 

 not the direct but the indirect source of the gold of quartz 



veins. If we admit as proven that sea water contains gold 

 in solution — and the balance of evidence appears, perhaps, 

 to be in favour of this view, althovigh it is by no means easy 

 to speak with certainty when such minute quantities are 

 in question" — the gold most probably exists therein as a 

 -haloid salt, possibly as a double chloride of gold and 

 sodium or potassium. This, although one of the most 

 stable salts of gold, is nevertheless so readily decomposable 

 by every reducing agent, including light and a comparatively 

 low degree of heat, that it would be quite inconceivable 

 that metallic gold should not be deposited from this sea 

 water, together with the sedimentary rocks forming on the 

 sea bottom, if it is allowable to take the ordinary labora- 

 tory reactions of gold salts as our guide. Modern chemical 

 research has, however, shown that the efifect of mass 

 action is too important to be disregarded, and that solutions 

 of extreme tenuity are subject to laws differing widely 

 from those governing the ordinary solutions with which 

 the chemist is in the habit of dealing. Moreover, we are 

 confronted by the difficulty that if this gold were preci- 

 pitable in the usual way, there would be none left in the 

 ocean, unless it were being redissolved as fast as it was 

 precipitated. The fact, if it be a fact, that the ocean 

 everywhere contains a minute but approximately uniform 

 quantity of gold, is in reality a fairly good proof that this 

 gold is not being precipitated. Having regard to the 

 circumstance that very many rock masses have been proved 

 to contain minute quantities of gold, it is, moreover, quite 

 unnecessary to go back to the ocean for a known source of 

 this metal. The evidence that gold does occur in various 

 rocks seems to be tolerably complete, and its presence 

 has been detected not only La sedimentary but also in 

 eruptive rocks. Whatever may be said about sedimentary 

 strata, eruptive rocks cannot well be supposed to have 

 obtained the gold they contain from sea water. In fine, 

 reviewing the facts before us a whole, it seems far more 

 probable that whatever gold is contained in the ocean has 

 been leached out of rocks, than that the rocks have derived 

 their gold from the ocean. 



We have so far cleared up two distinct points in our 

 investigation, and are justified in assuming — firstly, that 

 the gold of veins was introduced in solution, and secondly, 

 that its source may probably be traced to various rocks 

 of the earth's crust, and very possibly deep-seated ones, 

 such as eruptive rocks must have been originally. Two 

 other points yet remain : How was the gold dissolved out 

 of the rocks in which it existed ? and how was it dejiosited 

 from such solution ? To these latter two queries I fear 

 that our answer will have to be less definite than to the 

 former ones, much of our knowledge, if knowledge it is, 

 being only inferential. If we consider a fissure in the 

 earth's crust, lying below the region of the superficial 

 currents of underground water — the " vadose circulation " 

 of Posepny — we must La the first place look upon it as 

 necessarily filled with water, and in the second place we 

 must suppose this water to be La motion. The pressure Lii 

 the fissure will probably be less than in the deeper-lying 

 and adjacent rock-masses, and the greater temperature of 

 the lower parts of the fissure wLll give rise to convection 



* Whilst these pages were passing through the press, I 

 received a copy of the presidential address of Mr. Stanford to the 

 Society of Chemical Industry, delivered in July, in which that 

 gentleman says : " ^o analysis can give us any idea of what the 

 ocean really contains. . . . The presence of gold has not been 

 satisfactorily proved ; it was expected it might accumulate in the 

 copper sheathing of ships, and Messrs. Muntz obliged me with 

 specimens of old sheathing, both copper and Muntz metal. Mr. IngUs, 

 who kindly examined these for me, found both gold and silver, but 

 not in larger proportion than usual." — (Journ. Soc, Cheni. Ind., \o\. 

 XIII., No. 7, p. 697). H. L. 



