MODE XV. SIDEROUS INTRITE. 133 



STRUCTURE I. VARIOLITES. 



When the crystals, instead of being of an oblong 

 cubic form, as in porphyries, assume an oval, but 

 particularly a round shape, the rock may be aptly 

 styled a variolite, every denomination being use- 

 ful which saves circumlocution. 



The stones called variolites of Durance, being Variolites of 



Durance. 



pebbles rolled down by that river in Dauphiny, 

 belong to this article*. The prominence of the 

 round crystals of felspar, having a faint resem- 

 blance to the pustules of the small-pox, has oc- 

 casioned this appellation. Patrin f has minutely 

 described the variolites of Durance, as being in his 

 eye the same with the ancient green porphyry, 

 being a corneenne, or basaltin, fusible into a black 

 amel attractable by the magnet. The spots, of a 

 finer green, or sometimes white, are often sur- 

 rounded with two zones of these colours. Saus- 

 sure, whose description is very minute, 1539, 

 regards the globules as composed of that kind of 

 felspar which, being of a greasy appearance, like 

 one of the kinds of quartz, is called unctuous fel- 



* Faujas says that he found, near the village of Servieres, the 

 rocks which afford the variolites of Durance. For those of the 

 Drac, see Amygdalite. 



t i. 147. 



