^0 M. BE Hoff's Geological 



still, it is covered by porphyry; it is again found only near 

 Zella and Shul, remarkable for its singular structure, for the 

 large crystals of felspar it contains, and for its passages into 

 difi'erent rocks.* It is accompanied by primitive green- 

 stone, and covered by argillaceous schists and clay slate, 

 which occupy the place of mica slate in the eastern half of 

 the Thuringerwald. The schists are of a blackish or reddish 

 ash grey, contain an abundance of quartzose portions, either 

 as grains, veins, or beds, and very much approach the nature 

 of mica slates. Some penetrated by quartzose particles, are 

 worked as Whetstone slate. 



Porphyry is, of all the primitive rocks, that most abund- 

 ant in the Thuringerwald, and forms the most considerable 

 branches of two-thirds of the length of the chain. Begin- 

 ning with the west, that of the principal, or second formation, 

 which we are at present considering, has generally an argil- 

 laceous base (base d' argilolite), either red, greyish red, or 

 pearl grey, and contains very variably sized crystals of fel- 

 spar and quartz. The paste is sometimes ol a green colour, 

 and the rock becomes apparently a horustone porphyry, or 

 passes into a porphyry with a greenstone or trap base. 

 These porphyries constitute an assemblage of steep rocks, of 

 frequently many hundred feet elevation ; and afford pic- 

 turesque points of view in almost all the valleys. The moun- 

 tain of Rupberg is remarkable, from the prismatic recesses 

 the porphyry presents, as has been observed by Anschuez.+ 

 Very beautiful green porphyries occur round the Schneekopf, 

 and in the environs of Schwarzwald, Oberhof, &c. Porous 

 porphyries, whose cavities are often lined with small quartz 

 Crystals, are worked as excellent millstones. Their paste 

 moreover contains much quartz and felspar. A tolerably 



. * M. von Raumer regards the granite in the environs of Suhl, as well 

 as the porphyry that accompanies it, as belonging to the Sienite forma- 

 tion, and as resting on the slates ; he supports this opinion by his own 

 observations, and those mentioned in the work of M. Heim,onthe Thurin- 

 gerwald. (Geognostische Fragmente, p. 37, &c.) 



+ Uber die Gebirge itnd btcinarten des Kiirfurstlichen Scechsischen 

 Hennebevgs, p. 1 \i. 



