156 Notes on the Area of Intrusive Rocks at Bar go. 



and serving as a test for the value of the work done. I 

 propose, therefore, now to summarise the main results at 

 which I consider myself to have arrived, and I shall also 

 venture to suggest what seems to me, on broad lines, to be a • 

 possible explanation of the origin and formation of the 

 auriferous quartz reefs of the district in question. 



The quartz diorites of Dargo are evidently part of the 

 masses of plutonic rocks which underlie all Gippsland, and 

 which, by denudation, show at the surface in very many 

 places, and at all elevations, from the sea-level up to the 

 highest mountain tops. The Dargo area is one of a connected 

 series which extend in the lower paleozoic formations for 

 nearly fifty miles from the Tambo River, and then, if the 

 same conditions continue, are covered from sight by the Upper 

 Devonian rocks of the Avon River drainage area. The 

 general direction of these intrusive areas is, as a whole, to the 

 south-west, thus being approximately at right angles to the 

 normal strike of the Silurian rocks of the district. 



The immense forces connected with the intrusion of these 

 rocks into the sediments may be inferred from the observa- 

 tion that in places these latter have been deflected from their 

 normal strike, and lie alono-side the intrusive rocks in a more 

 or less east and west direction. This linear extension of 

 areas of intrusive rocks across the direction of the prevalent 

 strike I have also observed in places in the Omeo district, as, 

 for instance, at Swift's Creek. 



The prevalent strike of the Silurian strata in direction 

 west of north indicates a direction of compression acting at 

 right angles to it, and, I think, probably from the east. The 

 east and west diversion of the strata in the neighbourhood 

 of the intrusive area of Dargo is local, and may be due to 

 pressure exerted by the molten magma when being thrust 

 into the opening sediments. There was, I think, an elevation 

 of the crust, accompanied by an upward movement of great 

 force by the plutonic magma, which filled in and probably 

 thrust back the opening strata. The best explanation of the 

 phenomena which have imprinted themselves upon the rocks 

 is one in this case which points to subsidence in an adjoining 

 area to the eastward, probably beyond the present bounds of 

 the continent, acting against a rigid part of the crust of the 

 earth. By this the strata were forced to give way, and 

 their movement was assisted by the upward thrust of the 

 imprisoned magmas, acting under the weight of the sub- 

 siding area, as Huids under hydrostatic pressure. The weakest 



