CLABKE.] 
IGNEOUS AND CRYSTALLINE ROCKS. 
221 
2. PERIDOTITE, DOUGLAS COUNTY. 
The matrix of the nickel silicate at Riddle. Described by Dillcr and 
Clarke in Bull. 60, p. 21. 
The rock, which may be classed as saxonite, consists essentially of 
olivine and enstatite, with a little chromite and magnetite. Olivine 
predominates, and the enstatite forms less than one- third of the mass. 
Quartz, serpentine, and genthite are present as alteration products. 
Analyses by F. W. Clarke, record Nos. 811, 814, 792. 
A. The fresh rock. P. R. C. Ill, 
B. Separated olivine. 
C. The genthite found in the altered rock. Probably derived from 
olivine. 
Si0 2 
A1A • 
Fe 2 3 
FeO 
MgO 
CaO 
H. 2 Oat 110°. 
H 2 Oign.._ 
CrA 
MnO 
NiO 
41.43 
.04 
2.52 
6.25 
43.74 
.55 
4.41 
.76 
none 
.10 
42.81 
2.61 
7.20 
45.12 
none 
.57 
.79 
none 
.26 
36 
44.73 
1.18 
10. 56 
8.87 
6.99 
27. 57 
99.90 
3. CRATER LAKE. 
Rocks collected by J. S. Diller. Petrographic data, hitherto unpub- 
lished, supplied by Horace B. Patton for all except the last rock in 
the series. Analyses A to J, inclusive, by H. N. Stokes, record No. 
1671. 
A. Vitrophyric rhyolite, south edge of Llao Rock flow. Contains 
plagioclase, hypersthene, hornblende, and apatite in a glassy ground- 
mass crowded with augite microlites. 
B. Streaked rhyolite, near " Wine Glass " Grotto Cove. Contains 
plagioclase, hypersthene, hornblende, and magnetite, with black glass. 
A few small inclusions of basalt and hypersthene-andesite. 
C. Rhyolite, small dike immediately below Llao Rock. Contains 
plagioclase, hornblende, hypersthene, and magnetite, in a glassy 
groundmass crowded with microlites of feldspar and augite. 
