92 THE ROMAN COMAGMATIC REGION. 
rather granular, in some specimens rather felted, and its grain is also variable, the 
more granular fabrics being found in the groundmasses with the coarser grain. 
Microphenocrysts of leucite are common in the groundmass, in anhedral, usually 
rounded and occasionally irregular individuals, which show but faint double refrac- 
tion and carry few inclusions. Microphenocrysts of feldspar are quite common. 
These are soda-orthoclase, which sometimes shows a moire" appearance, and of lab- 
radorite. The relative amounts of these vary in different specimens; in some cases 
those of alkali-feldspar surpassing those of labradorite, as in the specimen from 
Monte Fogliano, while again the reverse is true, as in the rock from Monte San 
Antonio. The micro-groundmass shows numerous, anhedral prismoids and grains 
of augite and very few small, irregular grains of olivine. It is composed in large 
part of feldspar, apparently almost entirely a soda-orthoclase, which is sometimes 
in small laths with a felted fabric, and again in formless anhedra, both forms occur- 
ring together as well. There are the usual small magnetite grains and some small 
apatite needles. A small amount of interstitial nephelite is seen in some specimens, 
which is replaced in others by an equally small amount of glass base which is deter- 
minable with difficulty. 
Chemical composition. Two analyses were made of this type, neither of which 
has been published hitherto. With them in the table is repeated for comparison 
the analysis of the viterbal vulsinose from the Vico Volcano. 
Chemical Composition of Foglianal Vicose [Leucite-tephrite]. 
I. 
II. 
III. 
SiO 2 
54.8* 
O.QI4 
51.20 0.853 
56. 10 
A1 2 O 3 
iQ 59 
. IO2 
21 .21 . 2O8 
2O. 7? 
Fe 2 O 3 
1.66 
. OIO 
2.38 .015 
1 . 71 
FeO 
?.O4 
. O42 
3. 6? . O?I 
2 . IO 
MgO 
1 . 4O 
. O37 
I .00 . 050 
I . Id 
CaO 
d. Os 
. O72 
c . 42 Oo6 
Na 2 O 
2 O2 
. O/17 
2 II O2d 
2 86 
K 2 O 
TO. 4O 
III 
10. 63 . 113 
IO. 47 
H 2 O+ 
O. 77 
0.28 
O. 7O 
H 2 O- 
O. 4O 
O. IO 
o 30 
CO 2 
none 
none 
none 
TiO 2 
o. 73 
. ooo 
. 74 . OOO 
o 65 
ZrO 2 
o 01 
O. O? 
P 2 Oc.. 
O 17 
. OOI 
o ^6 .003 
O 2d 
SO,.. 
none 
trace 
MnO 
n d 
n.d. 
n d 
BaO 
o. 33 
100.30 
100.45 
100.73 
I. Foglianal vicose [leucite-tephritc]. Monte Fogliano, Vico Volcano, Ciminian District. 
Washington, analyst. 
II. Foglianal vicose [leucite-tephritej. Monte San Antonio, Auruncan District. Washington, 
analyst. 
III. Viterbal vulsinose [leucite-trachyte]. Sorgente di Grignano, Vico Volcano, Ciminian 
District. Washington, analyst. 
