84 Diorites and Granites of Swift's Creek, 



from waters not necessarily and immediately proceeding 

 from the surface, but connected either as water or water 

 vapour with the injection of the dykes or the intrusion of 

 the masses, then those deposits below the water-level would 

 be derived from below and from sources which cannot be 

 at present pointed out, owing to want of data.* The 

 metalliferous deposits below the water-level would then be 

 contemporaneous with the formation of the dyke, while above 

 the water-level the ores would have undergone changes due 

 to the ceaseless reactions set up by meteoric waters, and a 

 concentration of gold might take place. In fact, such 

 changes as are indicated as being in progress at the Alison 

 Mine, Costerfield, " where the highly saline water makes its 

 way through the roof of a drive, and then deposits a 

 mammillary crust of a brown colour, which, upon analysis, 

 was found to contain hydrated oxide of iron, oxide of anti- 

 mony, sulphide of antimony, gold and silica, with some 

 alkaline sulphates and chlorides. As the block of ground 

 is completely severed by workings in the course of the lode, 

 the water must come from above, the strata on either side 

 being dry."f 



The second hypothesis is, I think, most in accordance with 

 the facts observed as to the reefs in connection with dykes 

 or intrusive masses. 



At first sight these explanations would seem to be scarcely 

 applicable to quartz veins of the second class — -namely, such 

 as are found in the silurian sediments unconnected with 



* A discussion of this question more fully would lead me into the con- 

 sideration of regional metamorphism, which would be beyond the scope 

 of this essay ; but I may now point out that where sediments are invaded 

 by igneous masses, before they have been re-elevated after their formation 

 above the sea-level, the saline waters included in them during their deposi- 

 tion would supply not only a vast amount of heated water and water vapour, 

 but also materials for the regeneration of the sediments as mica schist, 

 gneiss, and granite. It may be broadly stated that the mineral constituents 

 of sea- water are the complement of the sediments. The experiments of Dr. 

 T. Sterry Hunt on the porosity of rocks proves how large an amount of 

 saline water may be included in uncrystallised sediments, and thus become 

 available, as I have suggested, for the regeneration of the sediments as 

 metamorphic rocks, and to provide the alkali for the soda and soda-lime 

 felspars. These triclinic felspars are a marked feature in the regional 

 metamorphic schists of Omeo. Professor Rosenbusch has shown that in the 

 contact schists of Bar Andlau the amount of water sensibly decreases as 

 they become more crystalline in nearing the contact. (Hunt's Chemical and 

 Geological Essays, p. 164. Eosenbusch's Die Steiger Schiefer, p. 256). 



t J. Cosmo Newbery, B. Sc, Analyst to the Department of Mines. Report 

 of Progress of the Geological Survey of Victoria, Par IV. p. 175. 



