Rocks and Ore Occurrences. 9 



rence at Lightning Creek is but an instance of the diffuse charging 

 of schistose rocks with auriferous material. In the case of Lock- 

 hart's Gap there is a diffuse charging of liolocrystalline rocks with 

 metalliferous minerals. In all these four cases the author would 

 however submit that the action by which they received their gold 

 was a comparatively deeply seated one, as indicated by the pres- 

 ence of quartz, a substance that is in all probability present in 

 the particular form in which we find it in lodes owing to a 

 comparatively elevated temperature of the water current that 

 carried the other mineral matter in course of deposition. 



These deposits thus differ in a very important manner from the 

 •auriferous sandstone reefs to which the author has elsewhere 

 drawn attention^ as occurring in Victoria, and that have 

 distinctly received their gold when much nearer to the surface as 

 is shown by the absence of quartz — that mineral when it occurs 

 in such reefs being found quite independently of the gold, and 

 offering no guide to the occurrence of the latter. The gold in this 

 case, although in silurian sandstone, was probably deposited at a 

 much less remote date than that of the occurrences forming the 

 subject matter of the paper and probably in late tertiary times. 



The rocks at Bethanga show the interesting case where 

 extreme earth pressure and local yielding has, owing to the work 

 thereby done upon the rock, given rise to a development of heat 

 so considerable as to bring about softening and a subsequent 

 recrystallization of the mass, an unstable condition of affairs that 

 relieves the earth stress- at a distance at the expense of the 

 place where the movement first starts, and which, when it occurs 

 near to a volcanic vent, is, the author would submit, the cause of 

 a flow of fluid lava and the explanation of many volcanic pheno- 

 mena. In the case under notice at Bethanga temporary planes 

 of weakness must be assumed to have been left that were 

 •disturbed again before the zone had completely cooled down to 

 the average temperature corresponding to its depth. Such planes 

 may indeed have been initially formed by the contraction of the 



1 "Some Auriferous Deposits," Report Australasian Assoc. Science, vol. viii. ilelbourne 

 Meeting, 1901, p. 227. 



'■i One place where such a state of strain in the strata is manifest at the present moment 

 is at Hillgrove, N.S.W. See official N.S.W. Report on Hillgrove Gold Field bj' Andrews, 

 1901, p. 18. 



