GREGORY.] 
AUGITE-ANDESITE. 
171 
veiy largest present, are represented. Optical measurements on some 
of the freshest pieces in the groundmass proved them also to be labra- 
dorite, although orthoclase must also be present, as demanded by the 
analysis. Besides the feldspars, augite grains are scattered abundant Ly 
throughout the mass, and small areas of brown glass, occasionally with 
bubbles, are also seen. The whole slide is darkened by iron dust, 
both magnetite and limonite or gothite. The rock is, however, in a 
remarkably fresh state, considering its age and position. Its character 
is unmistakable. 
Analysis. — The analysis of this rock, made by Dr. W. F. Hillebrand, 
of the United States Geological Survey, is given below (I), and analyses 
of well-known andesites from other localties (II- VII) are given for 
comparison : 
Analyses of andesites. 
Constituent. 
I. 
II. 
III. 
IV. 
v. 
VI. 
VII. 
SiO., . 
Per cent. 
61.40 
16.59 
2.13 
3.05 
2.73 
6.17 
3.83 
1.34 
.82 
.88 
.79 
None. 
Trace. 
.02 
Trace. 
.13 
.02 
Trace. ? 
Trace. 
.20 
None. 
? 
? 
None. 
Per cent. 
61.58 
16.96 
1.75 
2.85 
3.67 
6.28 
3.94 
1.28 
.24 
1.06 
.49 
Per cent. 
61.29 
17. 68 
6.03 
.30 
2.45 
5.61 
4.28 
1.38 
} .96 
.65 
Per cent. 
61.04 
15. 72 
5.03 
2.15 
3.61 
5.34 
4.02 
2.66 
.58 
Per cent. 
61. 45 
15.07 
4.46 
1.18 
3.02 
5.37 
4.00 
1.22 
1.23 
Per cent. 
61.17 
17.74 
1.78 
3. 51 
2.76 
5.90 
3.79 
1.71 
.83 
.45 
Per cent. 
63.25 
14.89 
6.54 
None. 
.82 
.59 
4.47 
4.78 
2.67 
Trace. 
A1 2 3 
Fe 2 3 
FeO 
MgO 
CaO 
Na 2 
K 2 
ir/>— 105-.... 
H 2 O+105<> .... 
Ti0 2 
Zr< >, 
OX)o-- 
None. 
V 9 0o 
NiO 
MnO 
Trace. 
.03 
Trace. 
Trace. 
.22 
None. 
.12 
.06 
.04 
Trace. 
BaO 
SrO . 
Li,<) 
.05 
Trace. 
P 2 5 
( '( )., 
. 14 
.61 
.78 
01 
Fl.. 
FeS 2 
(S0 3 .29) 

Losh . 53 
Total... 
100. 10 
99.23 
100. 63 
100. 15 
100. 14 
100. 00 
99.93 
