154 ORIGIN AND MODE OF OCCURRENCE OF GOLD-BEARING VEINS. 



often crossing each other in the bedding and joint planes of the 

 rock. 



The folding of strata into anticlinals and synclinals may also 

 lead to fractures somewhat similar to those which would be 

 formed by bending a piece of iron or wood, and this may cause 

 such cavities or fractures as those that contain the saddle reefs 

 at Sandhurst in Victoria. 



I have very little doubt that many fissures are increased in size by 

 the circulation of subterranean waters, and are sometimes worn into 

 irregular cavities and openings that are afterwards filled with ore, 

 and it is also quite likely that such chambers and pockets as seem 

 to have no inlet or outlet, may have been excavated by the action 

 of solvent waters that carried away the minerals through the 

 pores of the country rock, and the reason for believing this tc be 

 the explanation of such cavities will be seen further on when I 

 treat of lateral secretion. 



The theory that veins have been formed by a molecular 

 substitution and aggregation of minerals like pegmatite veins in 

 granite, must terminate with the fact that such veins have not 

 smooth and regular boundaries like the wall of lodes, but 

 gradually merge into the adjoining rock, large crystals of felspar 

 often occurring, part in the vein and part in the granite. 



The idea held by some that veins of quartz and lodes in general 

 have been formed upon natural planes in the slightly open or 

 fractured rock, and that the included mineral has by its expansion 

 during crystallization forced open the cracks, and by repeated 

 action of this sort quartz veins or other kinds of lodes of various 

 dimensions have been formed, can only be held on the supposition 

 that the lodes were formed very near the surface, and do not 

 extend to any depth. 



Experience has proved, however, that we have as yet no right to 

 limit the depth at which lodes may be formed in any way whatever, 

 as quartz veins and other lodes are worked for over 2,000 feet 

 below the surface, and certainly extended at one time for 

 thousands of feet above where the surface now exists, and have 

 by being broken up, together with the containing rock, supplied 

 immense alluvial leads, as in Victoria and elsewhere. 



The faulting and heaving of lodes by others which have been 

 subsequently formed shows that intense action has occurred, and 

 to think that the expansion due to crystallization of silica or any 

 other substance, could move a mass of rock even 2,000 feet thick 

 cannot for a moment be entertained. 



It is a noticeable fact that mineral lodes are in districts in 

 which the strata have been broken through by the intrusion of 

 igneous rocks or by other means, and that this is always the case. 



