Relations of Trap- Rocks with Ores of Copper. 21 



even sometimes give the rock a slaty sti-ucture, are parallel 

 to the planes of stratification. 



With respect to the geological situation of the schalstein, 

 we may mention a fact observed in the mine of Stangen- 

 waage ; namely, that the beds of schalstein are sometimes 

 contained between the slaty or calcareous beds, without be- 

 ing in immediate contact with the greenstones. This isola- 

 tion is pretty frequent, and, if we connect it with this other 

 fact, that the greenstone is still more frequently in imme- 

 diate contact with the slaty formation without intermediate 

 borders of schalstein, we come to the conclusion, that the 

 origin of the schalstein is not simply owing to circumstances 

 of contact. These rocks, as well as the beds of oligistic 

 iron, to which we shall afterwards advert, probably arise 

 from complex and prolonged phenomena of emanations which 

 have followed the eruptions of the trap. 



Let us now examine the conditions of the cupriferous re- 

 positories. These repositories consist of pretty numerous 

 veins ; some of them, continuous and ratlier wide, follow a 

 general direction, perpendicular to that of the beds, although 

 it is somewhat tortuous. These are the master veins. 

 Others, much moi-e numerous, are short and very narrow ; 

 their direction is generally oblique, and they are often con- 

 founded with the planes of stratification. 



The principal vein of Stangenwaage {haiipt-gang) tra- 

 verses in this way the series of all the beds of the formation, 

 and is consequently found in very heterogeneous media. The 

 principal contents are quartz, to which may be added, in 

 greater or less quantity, peroxide of iron, and the debris 

 coming from the rocks of the roof and walls. Copper pyrites, 

 pure, and often crystallized, are found in these vein-stones 

 [gangues,) and the experience of the miners has long since 

 proved, that the veins are never wide and rich in copper py- 

 rites, but when they traverse the greenstone and schalstein. 



The works of the mine of Stangenwaage demonstrate the 

 truth of this law. The miners have given the name of en- 

 richment {edle-mittel) to the parts which contain the copj-.er 

 pyrites in largest proportion ; now these enrichments exist 

 only when the veins cross the above-mentioned rocks. 



