2O 
THE ROMAN COMAGMATIC REGION. 
in percentages, and that molecularly the former may surpass the latter. The exact 
classifkatory position of this type is clear from the ratios. As regards class, order, 
and rang, it falls well within the borders of persalane, canadare, and nordmarkase ; 
but the ratio of the alkalis shows that the rock is transitional between the sodipo- 
tassic subrang phlegrose, in which it actually falls, and the dosodic subrang nord- 
markose. This type must therefore be called a nordmarkose-phlegrose. 
Chemical Composition 0} Ischial Nordmarkose-phlegrose [Augite-trachyte}. 
I. 
II. 
I. 
II. 
SiO 2 
61.88 1.031 
6l . 4Q 
TiO 2 
o . 69 o 009 
A1 2 O 3 
18.06 .178 
2O . O2 
ZrO 2 
0.08 
Fe 2 O,. . 
2 . 10 .OI4. 
2. II 
P 2 O,. 
0.07 .001 
O.O2 
FeO 
I . 38 .OIQ 
2 . 72 
SO 3 . .. 
o. oc 
MgO 
o. 61 . 015 
O . ?2 
C1 2 . 
O 3O OO.1 
CaO 
I . 15 . O2I 
1.88 
MnO 
n.d. 
Na 2 O 
6.89 .III 
2. -1Q 
BaO. . 
o 08 
O OI 
Ko 
H 2 O + 
7- 1 3 
100.52 
100.75 
H 2 O- 
\ -37 
0.46 
O=C1 
0.07 
CO, 
none 
100.45 
I. Ischial phlegrose (augite-trachyte). Marecocco, Ischia. Washington, analyst. Am. 
Jour. Sci., VIII, 1899, p. 289. 
II. Ischial phlegrose (augite-trachyte). Marecocco, Ischia. Fuchs, analyst. Tsch. Min. 
Mitth., 1872, p. 229. 
Or 
Norm of I. 
. . 7,Q. 48 ) ^ 
Ab . . 
A f 86 
.46. 6? \ 
ii 
Ne 
c.n ) 
HI* 
[ 5 
. 0.4.7 i 
S^ , 
Di 
-i. 24 ) 
Wo 
0.46 \ 3 ' 
70 
Mt 
< 
2.32) 
11 
/ 
. 1.37}- 4- 
77 
Hm 
. . 64. ) 

AD. . 
. O. 17 O. 
17 
Rest 
99.89 
o.e,S 
91.69 
Class 
Ratios of I. 
Sal 
' 'Fern 
= 11. 18 
Order 
Rang . . . 
Subrang 
F 
'L 
K 2 O'+Na 2 O' 
CaO' 
K 2 O' 
'Na 2 O' 
43 
0.64 
100.47 
* Hl=halite (Nad); cf. p. 15. 
The figures for some of the constituents in the analysis of Fuchs (II) closely 
resemble mine. That his determinations of the alkalis are not correct is indicated 
by the calculation of the norm of his analysis, which proves that these are not 
present in sufficient amount to satisfy the silica and alumina. 
Mode. The mode of the specimen analyzed was determined by Rosiwal's 
method, and is given in the table below. It must be observed, however, that no sodalite 
could be detected in the thin sections of the rock analyzed, and a test on the section 
by Lemberg's method with dilute nitric acid and silver nitrate solution gave a nega- 
tive result. It is possible that it was present in crevices of the piece analyzed, or 
else possibly existent as a glass, in which form it would be very difficult to detect 
