364 



THE GEOLOGIST. 



compact tin-lioldiiig ore-yeins (like tliose at Ehrenfriedersdorf in 

 Saxony) in and near the stock-formed masses. 



We here see four or five modes of vein-filling in connection with 

 one principal event — the eruption of a crystalhzed massive rock : 

 they are, crystallization out of the yet soft neighbonring rock, sub- 

 limation, infiltration, alteration, and injection in a hot fluid con- 

 dition ; and many of these modes of filling up are found combined 

 in one rock-fissure. 



Similarly situated to these tin- containing granites are the ore- 

 containing greenstones in the neighbourhood of Schwarzenberg in 

 Saxony, only the latter are mostly pressed into narrow parallel 

 fissures in the slate, and are therefore, although not more important, 

 much richer in metal than the former. I think I have already, in 

 1833, suf&ciently proved their injective origin.* In them also the 

 subHmation-, infiltration-, and alteration-products are added to the 

 original injected vein. When we find, in the same neighbourhood, 

 greenstone-veins as free from ore as the others are rich in it, we 

 must remember that the circumstances of the injection and cooling- 

 may have been extremely difierent. 



It is a distinguishing feature of all these plutonic injective and 

 secretion veins that their mineral species (which they contain) are 

 never carbonates, fluor-spar, or baryte, but hornblende, augite, 

 garnet, quartz, mica, and felspar, and such other minerals as usually 

 occur as constituents of massive rocks. 



The porphyry- veins also, in the environs of Freiberg, contain 

 manifold ores. In the vein which passes near the Muldener Hiitte, 

 pyrites is found thickly sprinkled ; and in a new quarry opposite 

 this same Hiitte there are a number of druses and vein-like cavities 

 in the porphyry, covered with coatings of pyrites, galena, blende, 

 calcspar, and baryte. These same minerals occur here not only in 

 lenticular clefts and fissui'es, but also entirely enclosed as small nests 

 in the porphyry, to which they evidently most intimately belong. 

 Similarly, the porphyry- veins of the Nonnen- and Fursten-waldes at 

 Kl. Waltersdorf are interpenetrated with many ore-holding quartz- 

 branches. 



* Erliuiteningen zur Geogii., Karte vou Sachsen, Tli. II, S. 217—246. 



