48 Correspondence — Mr. David Forbes, 



clusively as to whether a grey copper ore is entitled to the name of 

 Polytelite, or not. 



The Foxdale mineral described and analysed by me is a true Poly- 

 telite ; it contains nearly 14 per cent, of silver (or about 4500 ounces 

 to the ton), and agrees in all its physical characters with the most 

 characteristic specimens of this mineral. 



Quite prepared to admit that Polytelite may exist in quantity in 

 the Silver Vein Mine near Lostwithiel, Cornwall, I must, however, 

 confess that some of Mr. Davies' remarks rather tend to raise a 

 doubt in my mind as to this being in reality the case. 



Mr. Davies states he knows of " no accurate analysis having been 

 made of this ore," but informs us that " the last sample sold con- 

 tained 36J ounces to the ton," and that some years back ''the 

 average yield of silver was 68J ounces to the ton ;" and lastly, as 

 something remarkable, states that in one instance it was " 214 

 ounces ! " — Expressed in percentages these figures would merely be 

 about 0'11-0'21 and 0-64 per cent, silver — amounts which, mineralo- 

 gically considered, may be regarded as but traces of silver, not at all 

 conclusive of the presence of Polytelite in the ore. 



Metallurgists would not regard such ores as silver ores, but only as 

 argentiferous copper ores ; and many of the argentiferous copper ores 

 imported from South America contain far more silver than even the 

 richest of these, yet frequently do not contain a trace of Polytelite. 



"When, however, Mr. Davies adds that this " silver vein was 

 formerly worked for \he rich deposits of silver it contained, I sup- 

 pose in the state of sulphide" — does he not at once awaken a 

 suspicion that the silver percentage of these ores may, in reality, 

 be due to other sources than to the presence of Polytelite in quantity. 



When next in Cornwall, I shall be delighted to avail myself of 

 any opportunity of visiting this mine ; and could I procure an 

 authentic specimen of the mineral in question, should have much 

 pleasure in analysing it. Previous experience has, however, taught 

 me how little confidence can be placed in the genuineness of speci- 

 mens purchased of Cornish minerals, and I have no doubt but that 

 Mr. Davies' experience will have led him to the same conclusion. 

 Accurate mineral analyses requires such an amount of time, skill, 

 and expense, that before undertaking them it should be ascertained 

 with the greatest care whether the mineral in question is an authentic 

 specimen, or not David Forbes. 



11, York Place, Portman Square, "W., 

 December 23rd, 1867. 



British Fossil Cycads. — Mr. W. Carruthers being engaged in 

 investigating the structure of these fossils, would be obliged for 

 information respecting specimens from any British locality which 

 would enable him better to prosecute his enquiries. He reserves the 

 examination of the foliage to a future period, confining himself for 

 the present to the stems and fruits. Communications may be 

 addressed to him at the British Museum. 



