Sketch of the Thuringerwald. &1 



extended commerce arises from these works, the products 

 of which are known under the name of Krahwinkel mill- 

 stones. 



Advancing towards the east, a change takes place in the 

 nature of tlie porphyries, and they become generally of a 

 trappeau base. Yet further east, beyond a line drawn near- 

 ly from Gehren to Elsfeld, the porphyries entirely cease, 

 and give place to slates. 



The upper beds of the porphyritic rocks, those which are 

 contiguous to the amygdaloid (variolite) and red sandstones 

 that cover them, contain, in an argillaceous mass of a reddish 

 grey colour, besides the ordinary crystals of felspar and 

 quartz, cavities from the size of a pea to that of half a foot 

 rn diameter, but which are generally of the same dimensions 

 in the same district; the interior of them is either filled with 

 chalcedony or hornstone, or furnished with a layer of that 

 substance, lined inside by crystallized quartz, clear, or of a 

 violet or reddish white colour. There are also sometimes 

 crystals of carbonate of lime ; sometimes the cavity is filled 

 with powdery oxide of iron. The porphyry surrounding 

 these nodules, is penetrated by silex, which gives it greater 

 hardness than the rest of the mass ; so that it longer resists 

 decomposition, and numerous balls of it are found in the 

 neighbouring rivulets. This rock is named ball porphyry, 

 (porphyre a boules). 



Amygdaloid almost always accompanies the porphyry, and 

 especially the ball porphyry (porphyre a boules) ; its base 

 is of trap or wacke. The nodules are either in the form of 

 almonds, and filled with carbonate of lime or chalcedony, or 

 rounded cavities, void or lined with green earth, (chlorite 

 baldogee), calcareous spar, or crystallized quartz. 



Transition limestone is entirely wanting in the western 

 part of the Thuringerwald. It appears on the contrary on 

 the east under the grey wacke and schists that accompany it ; 

 it is quarried in the valley of Sorbiz, near Tceschnitz, and 

 known by the name of Schwarzburg marble. It is generally 

 of a dark colour, often altogether black, with red and brown 

 spots, and numerous veins of white calcareous spar. It 



