SALMON — ON THE FORMATION OF ORE-YEINS. 



389 



GENERAL CONSIDERATIONS ON THE FORMATION 

 OF ORE-VEINS, 



(Translated from the German of Professor Bernhard Cotta, of 

 Freiberg, with an Introdudorij Notice on the Study of Mineral 

 Veins and Metalliferous Deioosits, hij H. C. Salmon, Esq., Plymouth.) 



(Continued from page 368). 



These veins penetrate the crystalline schists, particularly the 

 gneiss, in those localities where the la.tter are largely penetrated by 

 porphyry. They also generally penetrate the porphyry ; only a few 

 exceptions from this rule serving to show that the porphyry- 

 eruptions continued into the period of the formation of the ore- veins. 

 These veins form three or four principal gToups, according to their 

 direction,* which groups in general differ both in age and in con- 

 tents. Still, all veins by no means show similar directions in 

 connection with similar contents, or the converse, only these pre- 

 dominant characteristics often coincide. Veins of distinctive con- 

 tents are almost as much confined to certain localities as they are 

 characteristic of definite directions. According to the contents we can 

 distinguish three or four paragenetic combinations of different ages, 

 but which often extend into one another in such a manner that one 

 fissure sometimes contains the products of two or three of these dif- 

 ferent periods. These paragenetic combinations of vein-contents are: 



1. Principally quartz and hornstone, with frequent fragments of 

 the neighbouring rock. There are also found, partly interwoven 

 with the quartz, and partly in numerous di^usy cavities. Brown-spar, 

 Manganese-spar, Calc-spar, Strontian, Fluor-spar, Rothgiltigerz, 

 Weisserz, Glaserz, native Silver, common Arsenical pyrites, Argenti- 

 ferous pyrites. Blende, Weissgiltigerfedererz, Iron-pyrites, &c.t 

 This so-called " great Quartz-formation" predominates in the fissures 

 in the neighbourhood of Braunsdorf and Siebenlehn. We find about 

 one hundred and fifty veins belonging to this combination. 



* Compare V. Beust's Gangkarte. 



t I have not considered it advisable to give the strict mineralogical names to 

 the mineral-species enumerated. The characteristic German ores I have given 

 in the original names. 



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