694 HENRY S. WASHINGTON 
dohyaline and hyalopilitic, composed of a colorless or slightly 
brownish glass thickly felted with minute, slender, prismatic 
microlites of an almost colorless mineral, which is most probably 
an aegiritic pyroxene. There are also some minute laths of 
alkali feldspar, but not a trace of hornblende could be detected 
in the groundmass. 
Chemical composition Two analyses were made of this type, 
and are given in the annexed table. 
The rocks are distinctly higher in silica and ferric oxide and 
lower in alumina and soda than the preceding type, lime being 
lower in the main occurrences, and ferrous oxide, magnesia, potash, 
and titanium about the same. Foerstner (p. 534) gives a partial 
analysis of a Zeneti “phonolite”; SiO,=67.8, Na,O=6.0, K,0= 
3.8. The high silica here is probably approximately correct, and 
is significant. 
A B 
Ope miIGt aches gery eee a ea 15.12 14.34 
Oo yeaia ke eaten Parmar Cla canes aan 27.80 26.13 
JN DY Gat ace ARANN eh a Lala eh ys crerSreas 33.01 33.01 
aN CHa pen ATG race rea cae II.55 12.47 
A] Bah canst ote Re De ere een eee 1.76 5-20 
WAY Anca ay een AU iano eee bc Se 3.38 1.42 
DY Gea eae irra. dar ean cara ine eens 1.62 0.93 
TDN age ee UE A ie ae a tes sea 1.67 1.82 
PACD Urthceeain ta nate tehen ce heataets ects ath 0.34 0.34 
97-25 95-70 
TREES ES etn eae S aeeeae eas He 3.48 4.00 
100.73 99.76 
The two rocks fall well within the subrang grorudose, 
II.4.1.3, though that of Punta Pozzolana is intermediate toward 
pantellerose, II.4.1.4. The chief interest of these norms lies in 
the fact that, in spite of the dominance of soda over potash 
shown in the analysis, the rocks are sodipotassic in their classi- 
ficatory position. This is due to the small amount of alumina 
which necessitates the formation of femic acmite. The amount 
- of alumina is too high, or that of soda too low, to permit of the 
formation of normative sodium metasilicate, which we shall meet 
with in the pantellerites. 
