82 



Diorites and Granites of Swift's Greek, 



2. Spaces filled by alteration products, forming crystalline 

 aggregates, in which quartz predominated. The smaller spaces 

 had the form and presented traces of hornblende. 



3. Crystals of arsenical and ordinary pyrites, surrounded 

 often by crystalline quartz. This example shows distinct 

 marks of alteration, and the Fe and As pyrites are evidently 

 secondary to the injection of the dyke stone. 



These instances illustrate the auriferous quartz veins con- 

 nected with dykes. They might be much extended by 

 references to Wood's Point and elsewhere ; but these given 

 will serve to show their mode of occurrence, and for com- 

 parison with the reefs of Swift's Creek. For comparison with 

 the diagrams just given, I now subjoin one illustrating 

 the manner in which I conceive the Swift's Creek reefs to 

 occur. 



Diagram No. 9.— Contact at Swift's Creek with Quartz 



Veins. 



(a) The intrusive diorite mass. 



(b.) The Silurian sediments (contact schists). 



(c.) Auriferous quartz veins. 



(d.) The plane of contact. 



The plane of contact would give passage to heated waters 

 or vapour accompanying the eruption of the diorites. It 

 would probably resemble contacts between the subterranean 

 masses of modern volcanoes and the adjoining sediments. It 

 is in such contacts, and the fissures connected with them, 

 that we may conceive metalliferous deposits to take place. 

 In the case of Swift's Creek all the reefs, with one exception, 



