684 HENRY S. WASHINGTON 
Rock Names Subrangs 
Kallerudose, I. 4. 1. 4 
Soday tra chiytesee eer : 
Rane Meee ee M5 5 tie A 
Pantelleritic trachyte..... Grorudose, II. 4. 1. 3 
Comendite ey ase Grorudose, II. 4. 1. 3 
Aegirite pantellerite...... Grorudose, II. 4. 1. 3 
: Varingose, IT. 3. 1. 3 
Hyal tellenite; eee: 2 
lige iar ate oe TE be, 8s, 
Basalte ee ae CAalMpLrOnose wUlnmcHonat 
SODA TRACHYTE, GIBELE TYPE (GIBELAL NORDMARKOSE) 
Occurrence.—Lavas of this type, the ‘“‘andesites” of Foerstner 
and Rosenbusch, constitute the mass of Montagna Grande and 
Monte Gibelé, covered in places with beds of pumice or flows of 
hyalopantellerite. The sheets of lava which make up the scarps 
of Montagna Grande are massive and often show a roughly colum- 
nar structure, while those of Monte Gibelé are, in general, less 
massive and compact. Along Costa Zichidi they form the upper- 
most flows, extending westward to the sea near Porto Scauri. 
Trachyte tuffs do not seem to occur. 
Megascopic characters——Lavas of this type vary from very 
compact forms to those which are somewhat vesicular. Strictly 
scoriaceous flows were not observed and even those which are 
vesicular show streaks of compact rock. The color is a light gray, 
the feel is rough and the texture highly porphyritic. 
Practically the only phenocrysts visible are of alkali feldspar, 
which form from 25 to 30 per cent of the rock, so that the type is 
dopatic. These are tabular, highly cleavable, with glistening 
surfaces, colorless and transparent, and are 1 to 2 cm. in diameter. 
A few small (1-2 mm.) phenocrysts of black augite are present, but 
they are so few in number and so inconspicuous as to be negligible. 
_ The groundmass is a light ash gray and almost aphanitic, though 
the lens reveals the presence of light and fewer dark particles, and 
it is clearly phanerocrystalline. In megascopic habit these rocks 
resemble so closely some from Ischia and the Phlegrean fields as 
to be almost indistinguishable from them. 
Microscopic characters (Fig. 6).—TYhe microscopic characters 
of this type from Pantelleria have been described by Rosen- 
