DOMAIN VII. COMPOSITE. 17 



NOME XV. JAD, SCHORL, GARNETS. 



A rock, which Saussure calls a mixture of 

 jad, sparry schorl, and massive garnet. It takes 

 a fine polish, and its large spots of red, green, 

 and yellow, form a beautiful effect*. 



NOME XVI. GRANITE AND CHALCEDONY. 



Chalcedony was chiefly found in amygdalites, 

 and by some supposed to be of volcanic origin. 

 Saussure f discovered this curious and important 

 rock near the city of Vienne, in Dauphiny. 

 On examining the stones employed in building 

 a peasant's cottage, he was astonished to find 

 that most of them were elegant chalcedonies, 

 more or less translucent, and mingled with leaves 

 of a beautiful yellow pyrites. Observing that 

 granite adhered to many of these fragments, the 

 rock was explored, forming the adjacent bank 

 of a rivulet called Bougelai. In some places it 

 filled up the accidental seams of the granite, 

 and in others formed nodules completely en- 

 veloped in that substance. The most common 



145. t 1634. 



VOL. II. C 



