176 METALLIFEROUS LODES, VEINS, MASSES. 



initiate abruptly, and consequently whether they fill cracks opened from the 

 surface towards the interior; but they are known to terminate in pointed 

 masses upwards, as at Joachimstal in Bohemia, and in many other places, 

 in small veins which have been worked. This circumstance leads us to 

 think that metalli'ferous veins have been produced by an injection from the 

 interior towards the surface, in the same way as the stony veins we have 

 mentioned. Besides, veins of this sort are strongly united to the others : 

 thus, at Pontgibaud, the same veins are sometimes granitic and sometimes 

 metalli'ferous; in many other places metalli'ferous veins accompany por- 

 phyritic veins, and even veins of basa'lt, as in Bohemia, and the two sub- 

 stances mutually penetrate each other, sometimes one and sometimes the 

 other being above. On the other hand, we very frequently find in the same 

 localities stony and metalli'ferous veins running parallel to each other, 

 sometimes crossing in different ways, one throwing the other aside, and 

 thus mutually producing more or less marked faults. Sometimes the stony 

 displace the metalli'ferous veins ; sometimes, on the contrary, the latter 

 turn aside the others: in everything they act exactly alike, and it is impos- 

 sible not to refer them to the same origin. It is also remarked that veins 

 generally follow great lines of dislocation of the crust of the earth. 



We find in metalli'ferous veins the influence of those which pass through 

 or accompany them, and which deposit, to a certain extent, substances not 

 previously observed. The influence of the rock passed through is seen in 

 metalli'ferous veins, as well as in those of trap; and it has been long known to 

 miners, that a poor vein in a determined bed at once becomes rich by pass- 

 ing into another, and the contrary : hence, the sudden success and unfore- 

 seen reverses in mining operations. 



22. Metalli'ferous masses being in 

 general but accumulations of small veins 

 running in all directions (fig. 286), or 

 an abundant dissemination in the midst 

 of a stony substance of the kind attri- 

 . Metalli'ferous b ute( ] to tne act j on o f fi re? [ t j s c } ear 



these deposits are produced in the same 



way as those just mentioned. These masses, the principal of 

 which present us with ores of tin, copper py 'rite's, and magnetic 

 iron, are chiefly composed of granites, porphyries, various mag- 

 nesian rocks, in which the ores are found. The metalli'ferous 

 mass of Zinwald, in Bohemia, is a particular granite enclosed in 

 a porphyry; that of Altemberg, in Saxony, is a porphyritic mass 

 enclosed in gneiss. The celebrated mass of magnetic iron of 

 Taberg, in Sweden, is a mass of diorite enclosed in gneiss ; that 

 of Cogne, in Piedmont, is a mass of serpentine driven into the 

 calci'ferous mica'ceous schist. 



23. Metalli'ferous lodes in regular beds, are merely veins which 

 have followed the stratification, as we observed in traps (fig, 283) 

 or deposits which were formed in contact with sedimentary beefs 

 and the fused matters that upheaved them. But we must not con- 

 found the masses and veins, just mentioned, with certain deposits 

 of o'olitic iron ores found in sedimentary formations. Among the 



22. Of what do metalli'ferous masses usually consist / 



23. What is meant by the term lode ? 



