LORD. I 
IGNEOUS ROCKS FROM SAN CARLOS FIELD. 
II. Average of five analyses of paniellerite from Pantellerm. 
98 
Constituent. 
Per cent. 
Si0 2 
68. 78 
S. -V.) 
5.12 
:;. 78 
1.44 
:;. 50 
7.16 
.15 
. 36 
Al.,(), 
Fe 2 3 
FeO 
CaO 
MgO 
K 2 
Xa .,< ) 
CuO 
H 2 
III. An 
ilysis of paisanite from Mosquez Canyon, 
Texas. 
Constituent. 
Per cent. 
Si0 2 
7:;. 35 
14. 38 
1.96 
.34 
.09 
.26 
4. 33 
5.66 
ALO, 
Fe A 
FeO 
MgO 
CaO 
Na 2 
K 2 
Tota 
1 
100. 37 
It will be seen that while the silica, iron oxide, and some of the 
ilkalies are essentially the same in the first two tables, the amount of 
?eO and Na 2 is smaller, and of A1 2 3 and K 2 is larger, in Analysis I 
han in Analysis II. 
This discrepancy in the chemical constitution of the two rock types 
s caused by the chemical dissimilarity of their amphibole constituents, 
ill other silicates being alike in both rocks. The barkevicitic horn- 
)lende (rich in A1 2 G 3 and comparatively poor in FeO and Na 2 0) of 
-he pantellerite from Presidio County is represented in the lava 
Tom Pantelleria by cossyrite, poor in A1 2 G 3 and very rich in FeO and 
The relatively large amount of potash in Analysis I would indicate 
dso a predominance of the potash feldspar molecule in the composition 
)f the anorthoclase in the Texas pantellerite. 
Comparing the analysis of this lava (Table I) with that of the paisa- 
] F. Foerstner, Ucber Cossyrite: Zeitsch. fur Krystnllog., Vol. V, 1881, p. 354. 
