210 
ANALYSES OF ROCKS, U. S. GEOLOGICAL . SURVEY. 
[no. 228. 
The following rocks arc from Shasta County, but not within either 
the Mount Shasta or the Lassen Peak areas. Collected by J. S. Diller, 
who furnishes the petrographic data. 
A. Dacite-porphyrv. cast fork of Clear Creek, 9 miles above French 
Gulch. Lassenose. Contains conspicuous phenocrysts of plagioclase, a 
few of quartz, and smaller ones of biotite and pyroxene, in a groundmass 
of quartz and feldspar. Analysis by J. E. Whitfield, record No. 970. 
B. Dacite-porphyry, Smiths Gulch, 6 miles up Clear Creek from 
French Gulch. Yellowstonose. Contains phenocrysts of plagioclase, 
quartz, biotite, and hornblende, in a groundmass chiefly of quartz and 
feldspar. Analysis by Whitfield, No. 971. Also described by J. P. 
Iddings in Bull. 150, p. 233. P. R. C. 90. 
C. Diorite, from Ono. Yellowstonose. Not described. Analysis 
by T. M. Chatard, record No. 1107. 
D. Metarhyolitc. The country rock near the Bully Hill mine. 
Rich in porphyritic quartz. 
E. Metabasalt. Country rock, wall of ore body, Bully Hill mine. 
Porphyritic quartz absent. 
Analyses D, E, by E. T. Allen, record No. 1981. The rocks are 
described by Diller in Bull. 213. 
A. 
66.30 
17.55 
2.19 
.55 
.97 
3. 1 2 
5. 15 
2. 45 
| 1 . 25 
trace 
.15 
B. 
C. 
D. 
E. 
Si0 2 
64.24 
18.67 
1.40 
1.96 
I.4S 
4.11 
4. 14 
68.10 
15.18 
1.34 
1.70 
2.06 
4.66 
3.71 
81.25 
9.03 
.63 
.40 
2.48 
trace? 
.25 
1.82 
1.09 
2.81 
.08 
trace 
.35 
49. 85 
A1 2 3 
17.00 
Fe 2 3 
4.02 
Fe( ) 
MgO..... 
CaO 
Na.,0 
5. 51 
7.65 
1.18 
4.78 
K 2 
H 2 at 105° 
1.71 
1.48 
none 
2.16 
H 2 above 105° ; 
Ti0 2 
PA 
s 
} 1 . 18 > . tiif 
.7(1 .35 
.08 .18 
6.65 
.97 
.10 
.07 
so 3 
.28 
.22 
.25 
CI. 
MnO 
BaO 
trace 
trace 
.20 
.06 
trace 
.05 
none 
Less 
99.96 
100. 20 
.05 
99.57 
100. 24 
.13 
99.94 
13 
100. 15 
100. 11 
99.81 
2. LASSEN PEAK REGION. 
Rocks collected by J. S. Diller, who has furnished the petrographic 
data. Nearly all are from the area covered by the Lassen Peak atlas 
sheet of the United States Geological Survey. The quartz basalts have 
been described by Diller in Bull. 79, and partly in Amer. Journ. Sci., 
3d series, vol. 33, p. 49. The analyses are so numerous that it seems 
best to divide them into subordinate groups. 
