166 'Di-.'Be-rger on Ibe physical Slrudt/re 



to the metallic veins, since they cross them, as I had an opportunity 

 of observing at different places in the mine 6f Dolcoath. 



I do not know if there are any other true veins posterior to the 

 cross courses, that is to say which cross them, and the direction of 

 which would in that case be from east to west. Did these occur, 

 it would point out three distinct periods at least, in the formation of 

 veins in Cornwall. Ought the small metalliferous veins which run 

 in the same direction with the cross courses, i. e. from north to 

 south, to be considered of contemporaneous formation with them ? 

 It is in a vein of this sort that the arseniate of lead is found. This 

 mineral has been lately discovered in the mine of Huel Unity, and 

 has been analysed by the Rev. \Vm. Gregor.* 



Although the cross courses are barren veins,f they are neverthe- 

 less, always dug into on each side, to ascertain whether they contain 

 any ore left behind by the older vein in the act of its being rent 

 asunder. A metallic vein interrupted by a cross course is more 

 generally impoverished than enriched. |' 



* Philosophical Transactions, part. ii. 1809. 



+ Cross lodes, cross courses, cross flookans, cross gossans, and contres or caunters, 

 ssre generally quite barren for tin and copper, but vvc have some few instances of cross 

 gossans being wrought for lead, though not to any great profit. Some antimonial veins 

 run also north and south. Pryce's Miner. Cornub. 



+ Charpentier thinks on the contrary, that a vein is sometimes enriched by meeting 

 witli another which is poor or even absolutely barren, or by meeting a vein that is 

 slightly filled up, and sometimes quite empty. lie gives as an example, the mining dis- 

 trict, called Le Prince Elector al Frederic Auguste, at Gross-Schirma, where a large vein 

 suddenly increases in richness, by meeting a very narrow vein, containing only a grey 

 clay, and without aiiy metallic substance whatever. Journal dcs Mines, No. xviii. p. 96. 



