230 



Hi chard Muller, from experiments conducted by him,, 

 established the fact that " solvent action is more facilitated 

 by increased pressure than by prolonged digestion," and hence 

 probably the speculation of J. C. Crawford, b who supposes 

 that mineral veins have been formed in the depths of the sea,, 

 and speculates thus : — " The filling of metallic veins, 

 particularly gold and silver, has chiefly taken place at a depth 

 of about 2,500 fathoms or over ; the precipitation may have 

 proceeded from metals in the waters of the ocean, or in passes, 

 or in water heated from below." According to Sonsdadt, 

 iodine in sea water is 'the agency which keeps gold 

 in a soluble and oxidised condition. 4 Dana c is of opinion 

 " the veins of quartz which contain the gold occupy fissures, 

 through the slates and openings among the layers which must 

 have been made when the metamorphic changes or crystalliza- 

 tion took place. It was a period for each gold region of long- 

 continued heat (occupying probably a prolonged age), and 

 also of vast upliftings and disturbances of the beds ; for tho 

 beds are tilted at various angles, and the veins show where 

 the fractures of the layers or the separations and gapings of 

 the tortured strata. The heat appears not to have been of 

 the intensity required for the better crystallization of the 

 more perfectly crystalline schists. The quartz veins could 

 not have been filled from below by injection ; they must have 

 been filled either laterally or from above. In all such 

 conditions of upturning and metamorphism the moisture 

 present would have become intensely heated, and hence have 

 had great dissolving and decomposing power ; it would have 

 taken up silica with alkalies from the rocks (as happened in 

 all Geyser regions), along with whatever other mineral 

 substances were capable of solution or removal, and the 

 vapour, thus laden, would have filled all open spaces, there 

 to make depositions of the silica and other ingredients it con- 

 tained. The mineral ingredients would have been derived 

 from the rock adjoining the veins or open spaces, or from 

 depths below through ascending vapours. By one or both of 

 these means the quartz must have received its gold, pyrites, 

 and ores of lead, copper, and other materials, all having been 

 carried into the open cavities at the same time with the silica 

 or quartz. The pyrite of the vein is usually auriferous, 

 showing that it was crystallized under the same circumstances 

 that attended the deposing of gold in strings, crystals, and 

 grains, and the same is often true of the galena." 



"With respect to the mine waters of Australasia, Messrs. 



b Trans. New Zealand Inst., Vol. IX., pp. 570-561. 



c Geol. Record, 1877. 



d. Erough Smythe. 



e Manual of Mineralogy and Lithology, 1879, p. 115. 



