230 M. DB RONNARD 071 the 



Mont Tonnerre, in the midst of the coal measures, which 

 very certainly cover the porphyry. There are proofs of the 

 latter superposition in many pits sunk in the coal measures, 

 between Kircheira-Boland and Orbis, on small veins of 

 mercury, and in which porphyry has been met with at a 

 slight depth. The porphyry of Mont Tonnerre is generally 

 of a very pale and often almost white colour. The crystals 

 of felspar, quartz, or mica, are not numerous, and the rock 

 is often a nearly pure petrosilex ; often also it apparently 

 becomes almost entirely siliceous; sometimes on the contrary 

 •the texture of the paste becomes less close, and the rock 

 passes into argilolite. I have not observed any true stratifi- 

 cation in it. At Langenthal to the N.W. of Mont Tonnerre, 

 a very regular and vertical vein of oxide of tin ore is worked 

 in the porphyry. At Imschbach not far from thence, veins 

 of silver, copper, and cobalt ores were formerly worked. 



2dly. The Konigsberg is less considerable ; it is yet much 

 more elevated than all the mountains of the coal measures 

 with which it is surrounded. The rock constituting it re- 

 sembles that of Mont Tonnerre, and like it is often a nearly 

 pure petrosilex. It contains numerous veins of mercury and 

 pyrites, accompanied with crystals of sulphate of barytes, 

 which have been and still are worked at the mines named 

 Wolfstein. On the sides of an adit level of these mines,* 

 the petrosiliceous rock occurs as an assemblage of inclined 

 prisms laid upon each other. Round Konigsberg, highly 

 inclined beds of blackish limestone are in some places seen, 

 which rest on the porphyry, and dip beneath the coal mea- 

 sures that surround it. To the W. of Wolfstein, near 

 Horschbach, the porphyry forms another elevated summit 

 in the midst of the coal country of the Glane. It is again 

 found on the banks of this river, near Ulmet, forming steep 

 rocks, and the coal measures are seen to rest on it.t 



* I have observed this prismatic disposition in the gallery of the 

 mines of St. Elias, and Christians-Gliick. 



+ I have not myself observed this fact; but I find it mentioned in the 

 Geognostische Studien of M. Rheinheimer, p. 82. 



