THE ROMAN COMAGMATIC REGION. 
Norms. 
Or 
III. 
. 1:2.82 
Ab 
... 23.06 
88.67-) 
An 
.... i 2 . 79 
C 89.24 
Ne 
. . . . 0.57 
\ 
HI 
0-57-' 
Di 
. . . . 3.67 
01 
. ... 0.63, 
4-3 
Mt 
-93 
11 
yo 
i-S* 
5.49 10.19 
Hm 
o i 
... 3 . 04 , 
AD . 
0.40 
0.40 
Rest. . 
99-43 
0.6? 
51-71 ) 
2I. 4 8[ 
13.62) 
1.98 
0.23 
4-32 
0.63 
4.18 
0.61 
0.32 
0.40 
86. 81 
4-95 
0.40 
89.02 
10.46 
49-48 
25-15 
12.23 
V. 
86.86 
100.08 
99.48 
Q-94 
100.42 
Ratios. 
3-9 
0.84 
o. 70 
0.91 
4.00 
0.67 
98.72 
v 
4-73 
5-6i 
0.67 
87.71 
III. 
Class 
Sal 
8.76 
Order 
Fem 
F 
i c ; . AA 
L 
K 2 O'+Na 2 O' 
Subransr. . 
CaO' 
K 2 O' 
3-7 
2.O7 
IV. 
8.51 
100.30 
V. 
7-97 
39.28 102.19 
2.92 
1.86 
3-19 
1.74 
The very close correspondence of these rocks, from near the extremities of the 
volcanic zone, establishes the type of bolsenal vulsinose with great definiteness. As 
regards class, the ratios approach somewhat closely to the border of dosalane, though 
not near enough to justify us in calling the type transitional. The ordinal position 
in every case is well within the limits, the amount of normative lenads being entirely 
negligible. The ratios determining rang are almost exactly at the center point in 
all three analyses, but as regards subrang all three approach the border toward the 
third (sodipotassic) division. This is especially true of V, which might be desig- 
nated properly a pulaskose-vulsinose, though it would seem to be a rather hair- 
splitting matter to call it a separate type on this ground, when the other represen- 
tative from the same volcano resembles it so closely. 
Mode. Complete estimation of the mode by Rosiwal's method was impos- 
sible, on account of the small size and confused arrangement of the constituents of 
the groundmass, as well as the error due to overlapping, although the phenocrysts 
could be measured with sufficient accuracy in the thin sections. The figures below 
are therefore based partly on Rosiwal measurements and partly on recalculation 
of the norm. 
Soda-orthoclase, Or g Ab 4 69-5 
Anorthite 6.1 
Andesine-labradorite, AbjAru n.g 
Augite 7.4 
Biotite i . o 
Ores 3.6 
Apatite 0.4 
Titanite o . i 
