570 SUPPLEMENT. 



appear veins of porphyry and of trap, or basaltin, 

 Veins of wacken are particularly frequent in the 

 metallic mountains of Saxony ; they traverse all 

 the other metallic veins, and are of course of a 

 more modern formation. Veins of grunstein ap- 

 pear near Bautzen. In the mountains of Schnee- 

 berg and Hartenstein, there are veins of clay-slate. 

 In the Pyrenees, Duhamel observed, not far from 

 Veins of the peak of Oncet, what he calls a bed of granite, 



granite. 



about nine inches thick, enclosed between two beds 

 of trap, which were themselves enclosed between 

 two beds of limestone. " We observed that the 

 inferior bed of trap disappeared, terminating in 

 the form of a wedge, so that the granite after- 

 wards reposed on the limestone. We also ob- 

 served that the latter is often penetrated by threads 

 of granite which appear on its surface, in the zig- 

 zag form ; and the granite also assumes the form 

 of nodules, being in all these circumstances firmly 

 adherent to the rock, which supports or encloses 

 it, forming with it a continuous body ; and there 

 is every reason to believe that it never penetrates 

 to much depth. This granite is in a great part 

 composed ot plates of felspar, more or less min- 

 gled with crystals of black schorl. The mica and 

 the quartz are thinly scattered. The same dis- 

 trict offered another phenomenon : we perceived 

 many real veins of granite, about an inch ia 



