232 
ANALYSES OF ROCKS, U. S. GEOLOGICAL SURVEY. [no. 228. 
8. ELDORADO COUNTY. 
A. Granitite, Placerville canal, one-third mile north of Ditch Camp 
No. 7. Alaskose. Collected by W. Lindgren, who reports it as con- 
taining biotite, orthoelase, plagioclase, and quartz. Analysis by 
George Steiger, record No. 1591. 
B. Granodiorite, 2 miles south of Silver Lake Hotel. Amiatose. 
Collected by Lindgren, who reports it as containing hornblende, bio- 
tite, plagioclase, and quartz. Analysis by Steiger, No. 1591. Analy- 
ses A and B are published by Lindgren in Amer. Journ. Sci., 1th 
ser., vol. 3, p. 306. 
C. Porphyrite, 1 mile southwest of Latrobe. Dacose. Published 
by Turner in 17th Ann., Part 1, p. 521. Contains abundant plagio- 
clase, less augite, calcite or dolomite, iron disulphide, a little chlorite, 
and secondary greenish mica. Analysis by W. F. Hillebrand, record 
No. 1432. P. R. C. 721. 
Si0 2 
A1 2 3 
Fe 2 3 
FeO 
MgO 
CaO 
Na 2 
K,0 
H 2 Oatl00°.... 
H 2 above 100° 
Ti0 2 
PA 
MnO 
StO 
BaO... 
C0 2 
FeS 9 
77.68 
11.81 
.72 
.51 
.18 
.72 
2.96 
5.00 
.04 
.27 
.14 
.10 
trace 
100. 13 
B, 
67. 45 
15. 51 
1.76 
2.21 
1.10 
3.60 
3.47 
3.66 
.14 
.63 
.58 
.12 
100. 23 
68.58 
13. 04 
.26 
3.40 
1.01 
3.22 
4.94 
1.90 
.16 
1.00 
.57 
.20 
.15 
trace 
.10 
1.31 
.15 
99.99 
