86 Diorites and Granites of Swift's Creek, 



words, the production of auriferous quartz veins seems to 

 have been in proportion to the igneous (volcanic) activity 

 of the period. 



General Conclusions. 



I have endeavoured to state so fully the evidence in re- 

 gard to the Swift's Creek district in its various geological, 

 penological, and mineralogical aspects that it is scarcely 

 necessary to do more than to finally state the conclusions to 

 which the careful consideration of this evidence had led me ; 

 and these conclusions are as follow : — 



1. The intrusion of the Swift's Creek granites and diorites 

 took place after the close of the Silurian and before the 

 commencement of the Upper Devonian periods, and was 

 probably connected with the volcanic activity of that time. 



2. The Swift's Creek granites and diorites were intruded 

 into the Silurian formations after the regional metamor- 

 phosis of the same, and the intrusion took place where the 

 metamorphic change ceased. 



3. The granites and quartz diorites were the earliest in 

 time, and were followed by the more basic diorites and 

 amphibole-gabbros. 



4. The intrusive igneous rocks disturbed the sediments 

 along the contacts, and partly absorbed them. They also 

 effected a metamorphic change in them analogous to that 

 effected by regional metamorphism. The contact metamor- 

 phism is most intense in the sediments immediately in 

 contact with the igneous masses, and decreases in intensity 

 outwards. 



5. The metalliferous veins were probably produced at the 

 time of the granitic and dioritic intrusions, and the lodes 

 were formed in the contacts or in fissures connected there- 

 with. 



6. Denudation and erosion, which have laid bare the 

 igneous masses, also set free the gold from the veins occur- 

 ring in the contact, and thus supplied the alluvial gold 

 deposits. 



Note — Since writing this paper I observe that Mr. Daintree has arrived 

 at somewhat similar conclusions as to the genesis of the auriferous reefs of 

 Queensland. See Note on Certain Modes of Occurrence of Gold in Austra- 

 lia, by Richard Daintree, Esq., F.G.S., Quarterly Journal of the Geological 

 Society, vol. xxxiv., p. 431. 



