

NOME XIX. GRANITE AND SLATE. 



of quite a new formation have been indicated by 

 Saussure*. In describing the mountains which sanssnre's 



remark^. 



bound on the north-west the valley of Valorsine, 

 he mentions that he found a mountain composed 

 of his roclie de come, which is sometimes basalt, 

 generally basaltin, sometimes basanite, some- 

 times magnesian basaltin, here called Saussurite; 

 and sometimes a coarse slate, or argillaceous 

 schistus, which seems here to be the casef. 

 " On observing this roche de corne in the spots 

 where it coalesced with the granite, I saw veins 

 of different breadths filled with a granite, which 

 was formed and moulded in their interior. The 

 largest of these veins is about three feet in 

 breadth, cutting at right angles the planes of the 

 layers of the rock, which it traverses; and the 

 uncovered part above the rest is about seven or 

 eight feet in length. The sides of this vein are 

 regular and parallel. The granite which fills 

 this vein is composed, like that of the mountain 

 to which it adheres, of grey quartz, white fel- 

 spar, and brilliant grey mica. This granite 

 presents little even slits or seams, rather indi- 

 cated than real, crossing each other in different 

 directions; which seems the effect of a begin- 



* 599- 601. 



t The corneus fssilis of Wallerius is hornblende slate, or slaty 

 siderite. 



