196 PROSPECTING IN CORNWALL. 



and so he had not the pleasure of exhibiting a more extended 

 series of these peculiar specimens. The chief characteristic, 

 and probably the most interesting, was the peculiar way in which 

 the gold was associated. The gold did not occur native, as in 

 other districts where gold was found in very large quantities, 

 but it occurred in connection with that rare element tellurium. 

 The discovery of gold and tellurium together was not new, 

 as, about twenty-five years ago, gold had been discovered in con- 

 nection with tellurium in the Boulder district. He shewed a 

 sample of sylvanite from that district, which he had found in the 

 Museum. It had been sent by him to the Eoyal Institution of 

 Cornwall several years ago. The gold as it occurred at Cripple 

 Creek was in the form of sylvanite and mineral calaverite, which 

 was the richest of all gold-tellurium minerals. Some experts said 

 at first that it was iron pyrites, but it was a compound of tellurium 

 and gold, and contained forty per cent, of gold. One interesting 

 point of this combination was that it did not occur in regular 

 well-defined veins and lodes, but rather in segregated masses, 

 — the result of intense thermal action. The rock which intruded 

 itself from the granite was andecite ; subsequently there was 

 another upheaval of rock called phonolite. The impregnation 

 of the rock of subsequent origin was the result of intense 

 thermal action, the extremely hot solutions probably containing 

 gold in connection with silica and fluorine. One thing which 

 was rather extraordinary was, that above the zone of oxidation 

 they had gold in combination with tellurium, simply as a telluride. 

 But, above the water-line, where water containing oxygen had 

 had the opportunity of oxidising this compound, they found that 

 gold had settled free, not in a form analogous to the ordinary 

 form of gold, — that was in bright yellow scales, — but in the form 

 of a red powder, which was not unlike gold produced by the 

 parting of an alloy of silver and gold, that was to say as a 

 brownish powder. In this way the miners had failed to 

 determine the existence of gold by the ordinary process of 

 panning and washing. Gold so light could only be made lustrous 

 by simple polishing. It was so light that it flowed off, and it 

 was impossible to find it by the prospector's plan of treating it 

 with the ordinary pan. 



