396 J. A. PHILLIPS ON MINERAL VEINS. 
that these processes were now going on, and that silica might erys- 
tallize slowly after deposition. He thought that a volatile mineral 
like cinnabar would be carried over by steam at a not very high 
temperature. He doubted whether silica and gold could be vola- 
tilized at such temperatures ; in most of these vents water in the 
form of spray appeared to be present, and gold and quartz were, 
he thought, brought up in solution by it. The great diffusion of 
the gold might be explained by it and the pyrites being formed pari 
passu. He had neyer been in Australia; but in California he had 
never seen an interstratified gold vein, but they were always 
true veins; and he did not think that quartz veins once formed 
became subsequently impregnated with gold. No vein with gold 
was ever practically of much value unless it had sulphides in it, such 
as pyrites or galena. 
