Sketch of the Thuringerzcald. 89 



side ; but is most frequently covered by porphyry and other 

 rocks. This granite, very uniform in the nature of its con- 

 stituent parts, varies greatly in their proportion and size. 

 The quartz in it often forms veins or geodes, sometimes 

 ferruginous, which have given rise to different mining works, 

 or rather researches. It also forms large masses that are 

 ■worked, when pure, for the porcelain manufactories. A 

 vein is worked in this granite at Heisenberg, near Ruhla, 

 formed of quartz, fluor spar, sulphate of barytes, and horn- 

 stone, containing oxide and carbonate of copper, with copper 

 pyrites. A part of this vein entirely consists of hornstone, 

 containing abundant fragments of granite.* 



The granite, properly so called, is surrounded by thick 

 beds of rocks, presenting passages from granite into gneiss, 

 or porphyry, sometimes by true gneiss and primitive trap 

 (araphibolites). The mountain of Trahberg, between 

 Weissenberg and Winterstein, is entirely formed of a rock 

 composed of felspar and hornblende. All these formations 

 are covered by mica slate. 



The gneiss and mica slates contain considerable beds of 

 greenstone (diabase), and of porphyry of a compact felspathic 

 base, passing, the author says, into hornstone, very different 

 from the porphyry in large masses, of which we shall prcr 

 gently speak, t 



All these rocks are traversed by numerous veins of quart? 

 and heavy spar, which were formerly worked, but are now 

 abandoned. Mica slate is not found to the east of Kleinsch- 

 malkalde ; but rocks of hornblende, felspar, and quartz, 

 occur in every variety of mixture and grain, and constitute 

 whole branches of mountains. A little beyond, the granite 

 disappears under red sandstone (alter konglomerat) ; farther 



' * This fact is analogous to that of the hornstone vein of Carlsbad. 

 (Journal des Mines, vol. 38, 341). 



+ An example is here seen of the most ancient porphyry formation 

 admitted by Werner. It is to be observed that the porphyry occurs here 

 equally in gneiss and mica slate, whilst in the Erzgebirge it has not been 

 found in the latter rock. (Journal des Mines, vol. 38, p. 440.) 



