Page:Quarterly Journal of the Geological Society of London, vol. 28.djvu/355

 diggings," by Mr, Richard Smith, of the School of Mines, Jermyn Street, made with the sanction and assistance of Dr. Percy (to whom

Fig. 15. — View showing the Intrusive Dyke of Diorite, with the Quartz-vein at the point of intersection with the Devonian Rods, at the Junction of Gilbert and Robertson Rivers.

I am indebted for the use of laboratory and reagents to complete the other analyses given in this paper), gave : —

Gold 89.920 Silver 9.688 Copper 0.128 Lead 0.026 Bismuth none. Iron 0.070 99.832

In considering the mode in which the gold was introduced into these veins, this constant association of silver is the chief difficulty to contend with. It is evident that the solvent and precipitant must have been able to perform their functions on each simultaneously. All experiments based on the precipitation of gold alone from its solutions afford no clue to the action which has taken place in nature, where the gold, silver, and other alloyed metals are entirely homogeneous.

No case has yet been established in our museums where the gold and silver are separated in the same specimen, as is seen in specimens of native copper and silver from Lake Superior.

In several reefing-districts in Queensland, however, we have con-

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