A 



139 



quartz*, of feldspar, or of fine-grained granite. 

 The gneiss presents, though more seldom, the 

 same phenomenon ; and near Wunsiedel *f, at 

 the Fichtelgebirge, I had an opportunity of exa- 

 mining crystal fours of two or three feet dia- 

 meter, in a part of the rock, which was now 

 traversed by veins. We are ignorant of the 

 extent of the cavities, which the subterraneous 

 fires and volcanic agitations may have produced 

 in the bowels of the earth in those primitive 

 rocks, which, containing considerable quantities 

 of hornblende, mica, garnets, magnetic iron- 

 stone, and red schorl (titanite), appear to be 

 anterior to granite, and of which we find some 

 fragments among the matters ejected by vol- 

 canoes. Those cavities can be considered only 

 as partial and local phenomena ; and their ex- 

 istence is scarcely any contradiction to the no- 

 tions we have acquired, from the luminous ex- 

 periments of Maskelyne and Cavendish, of the 

 mean density of the Earth. 



In the primitive mountains open to our re- 

 searches, real grottoes, those which have some 

 extent, belong only to calcareous formations, to 



* Gleichzeitige truemmer. It is to these stone veins, that 

 appear to be of the same epoch as the rock, that belong the 

 veins of talc and asbestus in the serpentine, and those of 

 quartz traversing the schistus (thonscbiefer) . Jameson 

 on contemporaneous Ferns, in the Mem. of the Werner, Soc., T. 

 hp* 



t In Franconia, South-east from Luchsburg. 



