212 
ANALYSES OF ROCKS, U. S. GEOLOGICAL SURVEY. 
[no. 228. 
2. DACITES AND ANDESITES. 
A. Gray dacite, Lassen Peak. Lassenose. Contains hornblende, 
biotite, plagioclase, quartz, scarce pyroxene, magnetite, apatite, and a 
glassy base, Analysis by T. M. Chatard, record No. 111. P. R. C. 82. 
B. Secretion in dacite, Lassen Peak. Composed chiefly of plagio- 
clase and hornblende. Analysis by Chatard, No. 110. 
C. Reddish dacite, Lassen Peak. Essentially like A. Analysis by 
ChUtard, No. 110. P. R. C. 82. 
D. Dacite, near the timber line, west base of Lassen Peak. Las- 
senose. Small phenocrysts of plagioclase and hornblende, with a few 
of quartz, in a reddish-gray groundmass containing much amorphous 
matter. Analysis by W. F. Hillebrand, record No. 668. P. R. C. 82. 
E. Secretion in I). Hessose. Composed essentially of plagioclase 
and hornblende. Analysis by Hillebrand, No. 669. P. R. C. 82. 
Rocks A, C, D, and E described by Diller in Bull. 150, p. 217. 
Si0 2 .. 
A1A- 
FeA 
FeO. 
MgO 
CaO. 
Na 2 
K 2 0. 
H 2 0- 
Ti0 2 . 
PA 
MnO 
SrO. 
BaO. 
69.5] 
15.75 
3.34 
2.09 
1.71 
3.89 
3.34 
.56 
trace 
100. 19 
B. 
58.97 
18. 60 
5.94 
6.89 
2.84 
3.05 
2.24 
1.35 
undet. 
C. 
68. 20 
16. 98 
3. 75 
2.07 
4.33 
2. 98 
1.52 
.44 
100. 27 
68. 32 
15. 26 
1. 66 
1.26 
1.32 
3.26 
4.27 
2.81 
1.37 
• 31 
.12 
.04 
trace 
.07 
trace 
100. 07 
55.14 
19. 10 
6.16 
.54 
4.23 
8.36 
3.71 
1.04 
.91 
.52 
.18 
.11 
.07 
trace 
trace 
100. 07 
