Augite Sod a- Granite from, Minnesota. — Grant. 385 
facies of the rock under consideration and of three other soda- 
granites are 
as follows: 
I 
II 
III 
IV 
V 
Si Og 
66.84 
67.42 
68.00 
70.69 
72.42 
Ti Oj 
0.40 
PeOg 
tr 
0.07 
0,20 
Al^Og 
18.32 
15.88 
16.18 
15.20 
13.04 
Fe, O3 
2.27 
1.37 
3.68 
3 76 
0.68 
FeO 
0.20 
1.14 
0.65 
2.47 
MnO 
tr 
0.09 
CaO 
3.31 
3.49 
4.05 
3.31 
0.66 
MgO 
0.81 
1.43 
0.95 
0.45 
0.58 
K2O 
2.80 
2.65 
2.04 
2.31 
4.97 
Naj 
.5.14 
6.42 
4.32 
4,69 
3.44 
H2 
0.46 
0.05 
0.56 
1.21 
100.05 99.92 100.49 101.07 100.37* 
I is the granite from Kekequabic lake, Minnesota (No. 551 G 
of the Minnesota Survey series) ; II is the prophyritic facies of 
the same (No. 86G); 111 is a soda-granite from Donegal, Ireland;! 
IV is the Aughrim (Ireland) soda-granite ;+ V is the rock from 
Pigeon Point, Minnesota.? In comparison with the last three 
analyses given above and other published analyses of soda- 
granitesll the rock here described is seen to be lower in the 
amount of silica and usually higher in soda than other granites 
of this series. The large proportion of soda finds expression in 
the composition of the augite as well as in that of the feldspar, 
as will be seen in the analyses given below. 
The feldspars are mostly' polysyntheticall}" twinned and show 
the optical properties of plagioclase, but a considerable number 
in the granitic facies of the rock are untwinned and seem to be 
monoclinic in character. Zonal structure is quite common in the 
phenocrysts of the porphyritic facies. On separating a powder 
of a fresh specimen of the granitic facies (No. 551 G) by means 
of Thoulet's solution, the larger proportion of the feldspar fell 
between 2.58 and 2.62, which would indicate that it was a mix- 
ture of the orthoclase and albite molecules, and the analysis of 
*Includlng traces of Lij O and CI and 0.15 of Ba O. 
f S. Haughton, Q. J. G. S., v. 20, p. 269. 
tW. J. Sollas, Trans. Roy. Irish Acad., v. 29, pt. 14, p. 471. 
gAmer. Jour. Sci.,(3) v, 37, p. 59. 
II Cf. A. Gerliard, Neuos Jahrbuch f. Min., Pet. u. I'al., 1887, J I, pp. 
267-275. 
