THE VOLCANOES AND ROCKS OF PANTELLERIA 693 
rather high powers, resolves itself into an aggregate of very small 
alkali-feldspar individuals, which vary in form from euhedral 
prisms to anhedral grains, imbedded in an interstitial cement of 
quartz. This last is often micropoikilitically developed,’ areas 
with uniform extinction inclosing the small feldspars. This 
quartz is doubtless the mineral called nephelite, unequivocally by 
Foerstner and doubtfully by Rosenbusch, but which the large 
ANALYSES OF PANTELLERITIC TRACHYTE 
(ZENETAL GRORUDOSE) 
A B Aa Bb 
‘S1Oha o oe 0 a ERE Oe NCR ee | 64.54 63°77 1.076 1.063 
ENLOs) 234 seo eee II.49 11.18 5 tng .I10 
IFCXHO.. avceeat olen eb eae aaa | Soul GeO2 .032 .031 
10QO) 5-Seous bo onchcne Senne 2.90 2.58 .042 .036 
IMIG O) «(pfs aa SiMe eee 0.89 Ons r .022 O13 
(CEXO) o.oo ecaucheek Haan eae eee 0.64 Te 7 Ole 025 
Na.0 ME etre or ascectieas cs 5-46 Bo KS .089 Moleje) 
IK0). tnd Sonne ieee 4.66 4.35 050 047 
ROC eee ee oe ce, fe TE; Veit 2.72 cae 
CO rie ose. Joes oe: 2.12 1.28 bie SP io 
IMO ie 6 chore a aes eee 0.90 0.94 .OII .O12 
Tid Oia 5 gE 8 Hi ee ee 0.08 ae ere ee 
PAO ka.o6'o 6 ote Cae ea eee 0.16 0.14 .OO1 .OOI 
* One's 6 6g Oe UE On eee 0.17 ae 
INGO). > oo eS Rcc nee er eaereee ©), 169} 0.26 002 
100.48 99.67 
A. Base of Costa Zeneti. H.S. Washington, analyst. 
B. Base of Punta Pozzolana. H.S. Washington, analyst. 
Aa. Mol number of A. Ba. Mol number of B. 
amount of free silica present in the norm shows cannot exist in the 
rock. Biotite is not present and no grains of magnetite were 
seen. 
Hyaline facies —A specimen of a hyaline facies of this type 
merits brief description. It forms a flow at sea-level at Punta 
Pozzolana.2, It is compact, very dark grey, and with very few 
feldspar phenocrysts visible. In thin section these feldspars show 
no feature worthy of special note, and phenocrysts of aegirite- 
augite and hornblende are extremely rare. The groundmass is 
1 Cf. P. Geijer, G. For. Stockh. Férh., XXXIV (1913), 51. 
2At Punta Pozzolana I found no rock corresponding to the “trachydolerite”’ 
mentioned by Prior from this locality. 
