PETROGRAPHY. 
75 
vom Rath, but it was not observed by Fuchs. Its identity was established by the 
close resemblance to other occurrences, the evidences of the birefringence and 
twinning, and the presence in many cases of the characteristic minute inclusions of 
augite which are centrally arranged. The groundmass also carries the usual small 
colorless augite anhedra, in prisms and grains, and some small grains of magnetite. 
The specimens typically are holocrystalline, those from Cavaliere showing a little 
nephelite cement, but those from L'Arso carry a little glass, either colorless or brown- 
ish and often dusty with minute indeterminable microlites. 
Chemical composition. Analyses of two specimens of this type are found below, 
one of which has already been published in incomplete form, together with one by 
Riva of another type of monzonose which may be called bolsenal from the descrip- 
tion by De Lorenzo, as well as an early one by Fuchs of the Arso rock, and also one 
of a monzonose from Montana. 
Chemical Composition of Arsal Monzonose [Vulsinite]. 
I. 
II. 
III. 
IV. 
V. 
SiO 2 
US. 22 O.92O 
56.75 0.946 
54.72 0.912 
57. 73 
> c ;.2-? 
A1 2 O 3 
18.43 .l8l 
18.03 .177 
19.60 .192 
17.8=; 
18.31 
Fe 2 O 3 
2 . O2 -OI3 
2.22 .014 
2.4<; .015 
4-4-4 
4.00 
FeO 
3 . 10 .043 
3 . O4 . O42 
3.09 .043 
^.QO 
2 .c6 
MgO. . 
2.7i; .060 
2 . O2 . 05 1 
i . 90 . 048 
1.77 
1.85 
CaO 
? . 7O . IO2 
4.68 .084 
c . oo . 080 
3.6<; 
3.62 
Na 2 O . . 
3. ?o cx6 
4 8s .078 
3. ?2 . o";6 
? . 77 
4.. O2 
K 2 O 
7.S8 .081 
C.O2 .063 
6.87 .073 
7.6<; 
6.43 
H 2 O + 
O. 46 ) 
1.84 
H 2 O 
J.^u , 
O 2O ) 
0.18 
2.08 
0.09 
CO 2 
none 
none 
TiO 2 
0.87 .on 
1.24 .016 
0.65 .008 
0.42 
ZrO 2 
o 10 
P 2 Or . . 
O.2I .CO2 
o . 34 . 002 
trace 
trace 
o.c8 
SO, . . 
O. II 
O.23 
Cl 
O. II 
0.05 
n.d. 
0.32 
Cr 2 O 3 
none 
MnO 
n.d. 
n.d. 
trace 
BaO 
0.07 
0.46 
100.41 
99 -3 8 
99-93 
100.85 
100.27 
I. Arsal monzonose [vulsinite]. Poggio Cavaliere, Lake Vico, Ciminian District Wash- 
ington, analyst. 
II. Arsal monzonose [trachyte, ciminite]. L'Arso, Ischia, Campanian District. Washington, 
analyst. Am. Jour. Set., VIII, 1899, p. 290. 
III. Bolsenal monzonose [" trachydolerite, " vulsinite]. Ejected block, Astroni Volcano, 
Phlegrean Fields, Campanian District. Riva, analyst. De Lorenzo and Riva, 
Alt. Ace. Sc. Nap., XI, 1902, p. 37. 
IV. Arsal monzonose [trachyte]. L 'Arso, Ischia, Campanian District. Fuchs, analyst. Min. 
Pet. Mitth., 1872, p. 230. 
V. Aspenal monzonose [gauteite]. Aspen Creek, Highwood Mountains, Montana. Foote, 
analyst. L. V. Pirsson, Bull. U. S. G. S. No. 237, 1905, p. 134. 
