28 GEOLOGICAL MEMOIRS. 



pears to have given occasion to Freiesleben to divide this group into 

 several formations, which however are nothing more than various de- 

 grees of development in one and the same fundamental character. 



The tin-ore is usually dissemmated in mmute points or grains, more 

 rarely in massive portions in the substance of the vein, hut has often 

 penetrated into the walls of the vein, sometimes in such a manner 

 that it is rather the neighbouring rock than the proper vein itself 

 which is worth working. 



In the mines at Altenberg the porphyry forming the walls of the 

 vein-mass itself contains tin, and it would appear that the metal has 

 crystallized out of the rock into the fissure of the vein. 



In some districts, as at Marienberg, Annaberg, and Oelsnitz, in 

 veins of this group, the tin-ore becomes less predominant, whilst mis- 

 pickel (Arsenkies), black blende, chalcopyrite, redruthite (vitreous 

 copper), bornite, malachite, black copper and kupferpecherz asso- 

 ciated with chlorite, appear in greater profusion ; so that the veins 

 assume entirely the character of the Seifen formation of Freiesleben. 



Other veins of this group, namely those north from Marienberg, 

 and some near iYnnaberg, Geyer and Sclmeeberg, produce particularly 

 much mispickel, black blende, chalcopyrite, and pyrite ; sometimes 

 also galena, but very little or no tin-ore. These appear in some 

 measure as connecting members between the pure tin-veins and the 

 veins of the pyritous-lead formation at Freiberg. The Thalheira 

 formation of Freiesleben belongs to this class. 



The veins of the tin-group, the number of which surpasses 400, are 

 the oldest in the Erzgebirge. They traverse granite, greenstone, and 

 often also porphyry ; but sometimes they are themselves intersected 

 by porphyries. 



2. The Veins of the Fyritical Silver ores are the most important 

 veins of the Erzgebirge. They are particularly numerous and fully 

 developed in the vicinity of Freiberg, and form together a large band 

 of veins {Grangzug)^ which extends from the left bank of the Elbe, 

 near Meissen, in a direction from north-east to south-west, past Frei- 

 berg and Nossen, as far as Langenau and Oederan, and finally appears 

 in the district of Wolkenstein and Drehbach. 



Quartz, diallogite and dolomite (brown-spar) associated with mis- 

 pickel, pyrite, black blende and argentiferous galena, fonn the charac- 

 teristic materials filling these veins, with which noble silver ores are 

 more or less commonly associated. But the abundance of these 

 minerals varies in the different districts ; sometimes quartz, sometimes 

 pyrite, mispickel and blende, sometimes dolomite and diallogite, are 

 the prevailing contents of the veins, and hence this group has been 

 divided by Yon Herder into the three follo\^•ing formations : a, the 

 noble quartz-formation ; 6, the pyritical lead-formation ; and c, the 

 noble lead or dolomite (brown-spar) formation. 



a. The nohle Quartz-formation (the Braunsdorf formation of Freies- 

 leben) is especially developed to the north and west of Freiberg. The 

 veins belonging to it, of which 150 more important ones are known, 

 form a long band about four and a half miles broad and fourteen miles 

 long between Nossen and Oederan. Their strike is mostly parallel 



