THE VOLCANOES AND ROCKS OF PANTELLERIA 705 
glass is very thickly sprinkled with small (1-3 mm.), rectangular, 
nearly equant phenocrysts of white glistening feldspar, which do 
not show any flow arrangement. They are in some cases so abun- 
dant as to be present in almost as great amount as the glass, but 
typically the rock is dopatic. A few perpatic forms were seen— 
black obsidians with very rare and small feldspar phenocrysts. 
These pure obsidians do not seem to form flows, but occur as blocks 
in the yellow pantelleritic tuffs. In all the specimens examined 
by me this black glass is brownish in thin edges, and I saw none of 
the green glass noted by Rosenbusch and Foerstner. 
Microscopic characters’ (Fig. g).—TYhe numerous soda micro- 
cline phenocrysts are mostly euhedral, in stout prisms parallel to 
c or tables parallel to 6 (oro), but a few are rounded as by magmatic 
corrosion and some are fragmentary. They are usually quite free 
from inclusions, but a few contain minute crystals of aegirite- 
augite or cossyrite. Phenocrysts of two kinds of pyroxene are 
present, both in very smali amount. One is an almost colorless 
or very pale greenish-gray diopside; the other a bright grass- 
green, distinctly pleochroic aegirite-augite. Both occur as stout 
prisms, but subhedral with rounded edges, and the former is likely 
to be much corroded. The cossyrite phenocrysts are more abun- 
dant than those of pyroxene and resemble those of the preceding 
type. No arfvedsonite was seen and lime-soda feldspars and 
magnetite grains are wholly absent. Olivine is also wholly wanting, 
except in a specimen from Cantina Ziton, from a flow south of, 
and apparently from, Fosso del Russo. Olivine phenocrysts (about 
2 per cent) occur in this in small euhedral or subhedral, slightly 
corroded ° crystals, carrying a few magnetite inclusions. No 
cossyrite occurs in this rock. 
The groundmass is highly vitreous, the glass being brownish, 
never greenish in my specimens. In most specimens this glassy 
groundmass is dohyaline, small prisms of alkali-feldspar, with 
fewer of cossyrite and augite, being abundant. A flow texture is 
always well marked, shown by the fluidal arrangement of the 
microlites, as well as by streaks of more or less crystalline ground- 
mass, some of which are almost holocrystalline and correspond 
to the groundmass of the Santelmal type. 
t Rosenbusch describes this type with the preceding (oP. cit., p. 85 2) 
