PETROGRAPHY. 
Chemical composition. Analyses of bolsenal vulsinose are available from two 
occurrences. Those of the Bolsena rock were made on material from the same flow 
but of different specimens. One has already been published, but another analysis 
was made, since the former was only the second complete rock analysis which I 
had made, and a test of my work at that time was desirable. The results are satis- 
factorily concordant, especially when it is considered that they were made on dif- 
ferent specimens of a somewhat eutaxitic lava. As none of the sample of powder 
from the first analysis was preserved, the figures for TiO 2 and P 2 O S given in II have 
been inserted in I, with proper corrections in the amount of ALjO^. This is not 
strictly accurate, but as both specimens come from the same flow, and the figures 
in question are small, the error can not be of importance, and the analysis as 
thus corrected and completed is undoubtedly more nearly in accordance with the 
facts than as it was originally published. The two analyses of the Astroni rocks by 
Riva have been used, as they show evidence of accuracy by correspondence with 
the descriptions and figures of the mode, and are satisfactorily complete. 
Chemical Composition of Bolsenal Vulsinose [Vulsinite]. 
I. 
II. 
III. 
IV. 
V. 
SiO 3 
C8 21 O.O7O 
C7 OC O 066 
58.08 o 968 
C7 c8 0.060 
A1 2 O 3 
18.88 .185 
TO. 11 . 180. 
19. ii . 187 
TO . 1Q . IQO 
18.80 184 
Fe 2 O 3 
A.. O7 .026 
3. O3 .OIO 
i . s? .023 
3.22 .020 
4. 77 028 
FeO 
O.87 .OI3 
I . 12 .015 
i.oo .014 
1.62 .022 
MgO 
O.o8 .02? 
I. 12 .028 
1.05 .026 
I. i 7 .029 
I . 2O . O3O 
CaO 
i.z8 .046 
7.O? .O7O 
1 . 76 . 067 
4.08 .077 
}. 84 060 
Na 2 O 
2.S7 O42 
1. IO . O?O 
2 . 84 . 046 
3.12 .050 
3. 16 OCT 
K 2 O 
Q. 17 .Oo8 
97 9 
O J 
8. ss .001 
8.86 .og<c 
8.68 .097 
8 . 70 . 080 
H 2 O + 
O. 54 
O. 54 
o. ?o 
o. 61 
H,O- 
0.74 
O. II 
O. II 
0.44 
0.78 
CO 2 
none 
none 
none 
TiO 2 
0.82 .010 
0.82 .010 
0.82 .010 
0.32 . 004 
0.50 .006 
P 2 O S 
0.20 .001 
0.20 .001 
0.20 .001 
O.2I .OOI 
0.28 .002 
Cl 
O. 17 .COS 
o . 03 . ooo 
MnO 
n.d. 
n.d. 
n.d. 
o. <?7 
100.09 
99.80 
99.92 
100.49 
TOO. 21 
So. CT. . . 
2 . ? 74 at 2 5 
I. Bolsenal vulsinose [vulsinite]. Below castle, Bolsena, Vulsinian District. H. S. Wash- 
ington, analyst. Jour. Geol., IV, 1896, p. 552. TiO a and P 2 O 5 from II. 
II. Bolsenal vulsinose [vulsinite]. Below castle, Bolsena, Vulsinian District. H. S. Wash- 
ington, analyst. 
III. Bolsenal vulsinose [vulsinite]. Below castle, Bolsena. Mean of I and II. 
IV. Bolsenal vulsinose [vulsinite]. Caprara, Astroni, Phlegrean Fields. C. Riva, analyst. 
De Lorenzo and Riva, Aft. Ace. Nap. Sc*., XI, 1902, p. 43. 
V. Bolsenal vulsinose [vulsinite]. Pagliaroni, Astroni, Phlegrean Fields. C. Riva, analyst. 
De Lorenzo and Riva, Alt. Ace. Nap. Sci., XI, 1902, p. 48. 
