744 



H. S. WASHINGTON 



2 £=40°-45° and the refractive index 7„a= i .65-1 .655. These 

 iigures are high and much resemble those of some biotites of 

 Vesuvius. There was not sufhcient material to make an analysis 

 of them. In this rock also there occurred rather abundant crystals 

 (1-3 mm.) of a pale, greenish olivine. The rock of Ghizo is a dark 

 brick red with many bronzy biotite tables. I was not able to 

 obtain any fresh specimens of this, so that for the present it may 

 be left out of consideration. 



Fig. I. — Analcite basalt, Scano 



Microscopic characters {Figs, i and 2). — ^In all these basalts, the 

 phenocrysts of augite and olivine are not very prominent in the thin 

 section. The olivines vary from o. i to 0.5 mm. in diameter, and 

 are generally anhedral, euhedral crystals being comparatively rare. 

 They are colorless and quite fresh, except for a thin border of trans- 

 parent bright-yellow alteration product, apparently aUied to idding- 

 site, the amount of which is never very great. There is never any 

 serpentinization. The augites are colorless, anhedral, smaller than 

 the olivines, and comparatively rare. One sees scattered through 



