ORIGIN AND DEVELOPMENT OF ORE-DEPOSITS. 377 



The galena of the district is almost always notably 

 argentiferous, ores running from 30 up to 100 ounces of silver 

 per ton being common. At times the production has been 

 considerable, yet it cannot be said that lead mining has ever 

 been a really important industry here compared with the mining 

 of copper, and still less as compared with tin. It has now 

 (1891) almost absolutely ceased to exist. 



A considerable number of rare minerals resulting from the 

 decomposition of galena have beea found in the gozzany 

 portions of the lodes, but rarely in workable quantities. As a 

 rock constituent lead ores have scarcely ever been seen in the 

 district, and on the whole it would perhaps not be far wrong to 

 reckon lead as about equal in quantity and in area of distribution 

 with zinc, though the areas are not quite coincident. 



Antimony. This element has usually occurred with lead, 

 and under like conditions ; mostly as a sulphide, and confined to 

 veins in stratified rocks of a fossiliferous series, at a distance 

 from the granite. It has always been far less abundant than 

 lead. 



In group 2 we have a number of elements very intimately 

 associated with each other, more particularly through the non- 

 metallic sulphur, which may have come in part from "deep 

 seated" sources, as is almost certainly the case with fluorine and 

 its associates of the first group. But there is a notable 

 association of some at least of the sulphuretted metals (lead, 

 and antimony) with the stratified rocks of a fossiliferous series. 

 It seems probable that at any rate galena and antimonite, and 

 possibly too part of the blende and chalcopyrite, may have been 

 derived directly from these rocks, or from others formerly 

 over-lying them and now denuded away ; though primarily 

 coming from deep-seated sources by means of ancient springs, 

 which mineralized the waters in which the rocks in question 

 were laid down. 



