THE VOLCANOES AND ROCKS OF PANTELLERIA 709 
north slope of Monte Sant’ Elmo—forming rather extensive flows 
from 2 to 5 meters thick, and accompanied by much scoria and 
ash. There are a few basaltic dikes cutting yellow pantellerite 
tuffs but these are of small size. 
Megascopic characters—These basalts present no unusual 
features and are of the common type, dark-gray to black rocks, 
aphanitic or nearly so, with few small phenocrysts.of dark-green 
augite and sometimes yellow olivine and fewer of feldspar. Most 
of the specimens are slightly vesicular and scoriaceous aa flows are 
common. The scorias are generally black, but sometimes reddish. 
About Cuddia Ferle small, ovoidal or fusiform bombs are found. 
Microscopic characters (Figs. 10 and 11).—The phenocrysts of 
feldspar are anhedral and either stoutly prismatic or tabular, 
parallel to 6 (o10). Nearly all of them are of labradorite, about 
Ab,An,, with the usual twinning lamellae, and a few show a border 
of more sodic material. There are some phenocrysts of soda- 
microcline, especially in lava from Cuddia Ferle, which carry few 
inclusions, mostly of glass. Subhedra of colorless augite, often 
in clusters, are fairly common. Olivine phenocrysts are rather 
more common than those of augite in the Ferle basalt, but olivine 
is wanting in that from Sant’ Elmo. It is highly euhedral, very 
fresh, with few inclusions of magnetite. The rock analysis and 
norm show that it is an olivine and not fayalite. 
The groundmass is typically basaltic, composed largely of 
thin plates of labradorite, grains of colorless augite, and consider- 
able magnetite. In the larger flows it is holocrystalline. No 
nephelite is to be found. 
A dike of basalt which cuts*the yellow pantellerite tuffs at the 
northeast end of Costa Zeneti merits a few words of description. 
It has an east-west trend, approximately radial toward Cuddia 
Ferle, which is about one and a half kilometers to the west. It is 
vertical, from 10 to 30 cm. wide, and has hardened and blackened 
the rather incoherent tuff for about 5 cm. on either side. The 
rock itself is jet black and aphanitic, very minutely vesicular, 
more coarsely so toward the borders, and is almost free from pheno- 
crysts, very small (1-2 mm.) feldspars being sparingly present. 
In the section thin tables of labradorite are prominent, augite 
