230 M. Amed^e Burat on the Variations of 



Oued Boussoussa, the veins containing the copper pyrites 

 offer it to view immediately, without decomposition, and with 

 a brilliancy which the water running over it often furbishes 

 anew in the bottom of the valleys. The same fact is ob- 

 served in the veins of the Valley of ChifFa, so that a vein 

 which has undergone those great alterations, of which we 

 have so striking an example in the copper veins of Rhein- 

 breitenbach, has not yet been found in that vast country. 

 In Germany, and even in the very region wliere this altered 

 vein of the Rheinbeitenbach occurs, we have seen some at a 

 depth of one or two yards from the point where they crop 

 out, in which the copper pyrites, galena, blende, &c., pre- 

 sented themselves immediately, and with all their metallic 

 lustre. 



Among the plumbiferous veins whose superior region con- 

 tains principally the phosphates and arseniates of lead, while 

 galena predominates in their deeper parts, we may mention 

 one of the zug veins of Silbach, near Holzappel, in Nassau. 

 This vein still contains a notable proportion of phosphate at 

 a depth of 50 yards ; and in its superior part, the phosphate 

 of lead was the principal mineral, while all the other veins 

 of the same zug were exclusively characterised by the ga- 

 lena. How could so important an alteration be produced in 

 a single vein out of four in which the physical conditions of 

 exposure to atmospheric agents, and the mode of formation, 

 are absolutely identical ^ If we compare the vein-stones of the 

 altered vein with those of the others which have undergone 

 no change, we find that the quartz, while compact in the lat- 

 ter, is carious and full of holes in the other ; we find that the 

 rocks des epontes, and the epontes themselves, which, in the 

 sound veins, have nothing particular in them, are, like the 

 quartz, penetrated with green and yellow phosphate, crystal- 

 line or earthy. On observing these quartzy veinstones, hard, 

 compact, and well separated from the mineral matter, become, 

 in a single vein, carious, porous, and penetrated with other 

 metalliferous principles ; and by studying this energetic ac- 

 tion, which has discoloured and penetrated the rocks, des 

 eponteSi with the same principles, we cannot avoid concluding 

 that so energetic a modifying action had operated upon the 



