336 Transactions. — Geology. 



chanical action, and particles transported by water-currents- 

 are of course much worn — generally to such an extent as to 

 make the original form unrecognizable. Whenever possible 

 the particles of gold were left in situ, and figured in this posi- 

 tion with a portion of the a<ihering quartz or other minerals. 



It is not the purpose of this brief outHne to treat in detail 

 the many theoretical questions relating to the formation of 

 gold and the causes of its patchy distribution throughout the 

 gold-bearing region of this pro\ince. We are not yet in pos- 

 session of a sufficient number of facts to answer any of those 

 questions. " Where the gold is, there it is not ; and where it 

 is not, there it is," has been said with some cause of the 

 Thames Goldfield, and we must be satisfied with this para- 

 doxical explanation until further researches on the spot and 

 in the laboratory allow us to come forward with substantial 

 evidence. 



Gold is very widely distributed within the boundaries of 

 Ohinemuri. Probably all the minerals which are atiriferous 

 in other districts also bear gold in the Ohinemuri region. Xo 

 careful examination of several species, which are generally very 

 small, even microscopical, has yet been made. The mineral 

 most productive of gold is iron-pj-rites, and the microscopical 

 invesrigations support the theory that most of the gold of the 

 Thames and Ohinemuri districts was originally deposited as a 

 constituent of the pyrites. It is invisible in the pyrites, but it 

 becomes visible when decomposition takes place, though evi- 

 dently not in the original (molecular 7) form. The minute par- 

 ricles unite into granular or vermicular masses, which may be 

 found in the crust of oxide of iron enveloping a nucleus of but 

 incompletely-decomposed sulphide. Through some agencies not 

 3'et known, the gold set free is generally removed in a soluble 

 state, and deposited, simultaneously with quartz, in veins, or, 

 after the formation of quartz veins, in fissures, &c. Thin 

 coatings on ferruginous minerals may have been produced 

 through some electrolytical process. These dehcate coatings 

 were undoubtedly precipitates from solutions containing a 

 considerable amount of gold and other minerals. A portion of 

 the gold in quartz veins has apparently been deposited by 

 mechanical means, though it is difficult to see how it could 

 find its way through the compact rocks. 



ilost of the Ohinemuri gold is more or less crystalline. 

 As cr}"stals are always distorted or elongated, when free, or 

 the faces sUghtly cui-ved. In ' some cases this may have been 

 caused thi-ough contact with hard fragments of quai-tz dm-ing 

 compression of the rocks, or after its isolation. Mostly, how- 

 ever, the intact finely grantilar sui-face indicates that the 

 cr}'stals were formed in this imperfect condition. No perfect 

 octahedron was discovered — generally but a small portion of a 



