120 Proceedings of the Royal Society of Victoria. 



raneous with the metamorphism of the strata. At the Golden 

 Mountain Mine, at Bonnie Doon, gold has been mined at the 

 contact of granite with Upper Silurian rocks which are altered 

 by contact metamorphism but a short distance from the 

 junction. I consider that the granite intrusions of Doon took 

 place at a later period than the granitic intrusions of Corryong and 

 Glen Wills ; because here Upper Silurian rocks are altered while 

 at Wombat Creek they are not. From the consideration of 

 dykes we may obtain a certain amount of evidence bearing on 

 the age of some quartz veins. In the Upper Silurian Strata 

 the greater number of auriferous quartz veins are associated 

 with dykes, notably diorite ; they occur in, and across, and 

 adjacent to the dykes, and are subsequent to them. In the 

 Lower Silurian rocks the reefs are not as a rule connected with 

 dykes, but in some places ancient granitic dykes fault reefs, which 

 are the older. At Wombat Creek granitic dykes occur in the 

 Lower Silurian rocks but were not noted in the Upper series ; 

 and if sections were available dykes might perhaps be seen to 

 intersect the Lower rocks but to stop at, and not enter the Upper 

 series, just as in the Werribee Gorge a quartz-porphyry dyke is 

 stated in a note on the quarter sheet of the Geological survey of 

 that locality to intersect the Lower Silurian rocks but not to 

 penetrate the overlying beds of glacial conglomerate. 



In a mining item published recently by one of the Melbourne 

 dailies, the statement is made that alluvial gold will not be found 

 far south of the northern fringe of the Pitfield Plains as the 

 marine strata commence there and the alluvial will not extend 

 into them though the reefs may continue further south. I 

 consider that along some of the belts of auriferous country, 

 especially when the gold in the reefs has been of a nuggety 

 character it may pay in places to follow the line of reefs under 

 the marine wash and work for alluvial where the gold has been 

 concentrated by local conditions.^ To summarize briefly then : 

 I consider that we have no fear of any Tertiary gravels being 

 poor in gold for the reason that auriferous quartz veins were not 

 in existence when they were deposited but that possibly the 

 later formed gravel beds will be richer in gold than the earlier, 



1 Murray, I.e., p. 158. 



