PETROGRAPHY. 
guishing as a whole or in separate twinning lamellae simultaneously over consider- 
able areas, which inclose poikilitically small augites and magnetites. These obser- 
vations I have been able to confirm in sections kindly shown me by Signor Sabatini, 
but have been unable to discover any such cases in the specimens collected by myself, 
either from the Latian or Hernican districts. In all my specimens the leucite areas 
are dark between crossed nicols, or show the characteristic twinned structure, and 
interrupt the continuity of the lamellae of the inclosing feldspar. 
Chemical composition. An analysis of this type was made on a specimen from 
Gli Arcioni, near Rocca di Papa,* in the Latian District, and is as yet unpublished. 
Chemical Composition of Hernical Braccianose [Leucitite]. 
I. 
II. 
III. 
SiO 2 
47. 2O 
0.787 
47.80 o 
708 
47.6? 
ALO, 
17.66 
. 173 
17.87 
T7C 
18.13 
Fe 2 O, . 
2. CT 
. O2 2 
4 .07 
O3I 
2 .63 
FeO .... ... . 
4. SO 
. 063 
3. 64 
oco 
6.48 
MgO 
A. 2O 
. IOC 
7.68 
OQ2 
4- 10 
CaO 
0. C2 
. I 7O 
8.70 
ice 
Q.OI 
Na 2 O 
2 . 2? 
.036 
2.60 
O42 
2.78 
K 2 O 
7.6? 
.O8l 
8.23 
087 
7-47 
H 2 O+ 
O. 72 
0.61; 
O. 13 
H 2 O 
O. C7 
O. II 
CO 2 
none 
none 
none 
TiO 2 
1 . 10 
.QIC 
o. 77 
.OIO 
1. 1* 
ZrO 2 
0.04 
O.O2 
O.O2 
P 2 Oc. . 
o. c8 
.OO4 
o. 36 
. GO"? 
O. CO 
SO,. . 
none 
none 
none 
s 
none 
none 
none 
MnO 
n.d. 
n.d. 
n.d. 
BaO 
o. io 
0.28 
0.24 
99.76 
99.68 
100.47 
Sp- gr. 
2.781 
I. Hernical braccianose [leucitite]. Arcioni, Rocca di Papa, Latian District. Washington, 
analyst. 
II. Galeral braccianose [leucitite]. Near Crocicchie, south of Lake Bracciano, Sabatinian 
District. Cf. p. 109. 
III. Vesbal braccianose [leucite-tephrite]. Lava of 1872, Mount Vesuvius. Cf. p. 104. 
3 
Norm of I. 
Or 17.24 
An 15.57 
Lc 2I - 8o i.32 02 
Ne 10.22 t 32- 
Di 22.46 
II 2.29 
Mt 5.10) g 
01 2.28$ 7 '3 
Ap i . 34 i . 34 
64.83 
33-47 
Class . 
Order . 
Ratios of I. 
Sal 
' 'Fern 
F 
L 
Rest. 
Rang 
Subrang. . 
99-82 
* Cf. Sabatini, Mem. descr. Carta Geol. Hal., X, 1900, p. 260, fig. 58. 
98.30 
. 1.52 
CaO' 
K 2 O' 
Na 2 O' 
= 2.08 
= 2.25 
