of Devonshire a?id Cornwall, 169 



A vety singular and very anomalous combination of tin with 

 sulphuret of lead is found in the mine of Heavas in the parish of 

 St. Mewan. There is also a vein at Marienberg in Saxony, in 

 one part of which ores of tin are found, and in another, ores 

 of silver.* Are we to infer, that in some cases the tin veins already 

 formed have been rent, and the new fissures filled with ore of a 

 later formation ; or are we to admit, that there are tin formations 

 of different ages ? 



The cobalt united with tin, found in Wherry mine in the parish 

 of Madron, belongs very probably to the oldest formation of cobalt, 

 the same as that of Gieren in Silesia, which is in a mountain of 

 mica-slate ;'f for the veins of cobalt in secondary mountains are of 

 very recent formation. 



The tin is accompanied with arsenical pyrites, copper pyrites, 

 and even blende, as in the mine of Trevascus. Arsenical pyrites, 

 according to Werner, is of very old formation, although produced 

 at different ages ; for we find it (he says) with tin, with galena » 

 sometimes, though rarely, with copper pyrites, and also V\^ith arseni- 

 cal silver ore.;}: It is not usual, he adds, to find copper pyrites with 

 blende, but very frequently this last accompanies galena. 



Copper occurs in various forms in Cornwall, independently of Its 

 combinations with tin, with cobalt, and with silver : viz. in the 

 native state,§ in the states of red oxide, blue carbonate, green car- 

 bonate, sulphuret, grey antimoniated ore, and arseniate. The sub- 



* Nouvelle Theorie dela formation des filons, p. 106. 



+ Ibidem, p, 179. 



X Nouvelle Theorie de la formation des filons. 



§ «* Native copper is frequently found in our mines near the clay or surface, or 

 " commonly but a few fathoms deep; though there arc some few instances of its being 

 *' found very deep, particularly in the mine of Cook's Kitchen." Pryce's Miner. 

 Corn. 



