and their Contact Zones. 83 



that have been mined upon comply with the requirements 

 of such an hypothesis. The exception, as I have before said, 

 is the Caroline Reef, which penetrates the nodular 

 argillaceous schists at a distance from the granitic contact. 

 Such fissures as those indicated would tend to pass upwards 

 through the schists, but would not, I conceive,, be found to 

 penetrate downwards into the consolidated igneous mass. 



Denudation and erosion acting along the contact would 

 suffice by the wearing down of successive small auriferous 

 veins to supply the large amount of alluvial gold which has 

 been found at Swift's Creek. 



In all the cases now given, including those at Swift's Creek, 

 the bounding rocks, as well as the reefs themselves, are more 

 or less highly impregnated by pyrites, which are often richly 

 auriferous.* At Swift's Creek, in addition, there is locally 

 some amount of sulphides of lead, copper, and zinc. 



In the upper parts of the veins percolating surface waters 

 and atmospheric influences have decomposed the sulphides, 

 while below the water-level these usually remain unaltered. 

 It has further, according to my experience, been frequently 

 found that the amount of gold has been relatively larger in 

 the vein above the water-level than below it. Two explana- 

 tions might, I think, be given of the presence of the 

 metallic sulphides and of the gold— (1) That the ores and 

 gold had been collected in solution from the superior or 

 from the bounding rocks ; (2) that they had been trans- 

 ported in solution from below upwards. I think that 

 a third alternative — namely, the injection of the ores and 

 gold with the molten substance of the dyke — need not 

 be considered. In either of the two former alternatives 

 the vehicle must, I think, be held to have been water or 

 water vapour. 



If we were to assume that the gold and metallic ores have, 

 together with the quartz, been deposited in these fissures 

 from percolating surface waters which have abstracted them 

 from the superior or bounding rocks, we must then further 

 assume that this process is constantly operative to keep 

 pace with unceasing denudition of the surface, and that a 

 concentration of gold has taken place above the water level. 

 If, on the other hand, we were to assume that the deposition 

 of ores and gold took place with the quartz in these fissures 



* Tailings taken from Mr. Forsyth's mill at Swift's Creek gave, according 

 to an assay by Mr, J. C. Newbery, at the rate of over 70 ozs. of gold per ton. 



