354 Proceedings of the Royal Society of Victoria. 



The action of sea water on the sulphide ore is held by the 

 writer to sufficiently account for the phenomena of the 

 secondary ores of Mt. Morgan without calling in the aid of 

 thermal springs. Besides the thermal spring was meant by Dr. 

 Jack to account for the origin of the siliceous skeleton of the 

 sulphide ore which he then called sinter ; but this skeleton 

 has now been traced downwards, and proved to be the upper 

 leached portion of siliceous sulphides. 



It Avould not be necessary to invoke the aid of a thermal 

 spring if sea water could accomplish the work, for it is certain 

 that this spot was covered by the sea or a lake about the time when 

 the violent disintegration was at work, for as soon as the sands 

 and clays had re-settled in the basin, leaving a oavity in the 

 centre where the activity lasted longest, then horizontal beds 

 of Desert Sandstone were deposited, and these were piled up 

 to a height of 100 feet or more within the centre of the basin, 

 the ends of the beds resting on the sands, etc., of the secondary 

 ores, and this accumulation went on until such horizontal but 

 much false bedded sandstones were built up for perhaps 

 hundreds of feet above the top of the Mount as presented Avhen 

 mining began. These accumulations of sediment went on until 

 the conditions changed, and tlie sediments emerged from the 

 sea and were exposed to the air. Since then extensive denudar 

 tion has been at work, removing the cover of sandstone from 

 a great area about Mt. Morgan, leaving the plug on the Mount 

 itself because it was protected from wear and tear by being 

 countersunk in the secondary ore. These denuding forces are 

 still in full activity, carving the valleys deeper and lowering the 

 summits and ridges. 



It is iDrobable that the actual disintegration and subsequent 

 re-deposit of the secondary ore did not occupy any very long 

 period; the very fierceness of the action would imply a rapid 

 completion, and no doubt most of the gold from the ore dis- 

 integrated was thrown down again within the basin, but this 

 Avould not account for all that was found there. 



Some small proportion of the gold was certainly carried away 

 in the slimes or "overflow,"' and assays of this "overflow" 

 material were said to yield small assays of gold. But if a little 

 thus escaped, it is probable that the secondary ores were 



