138 ANALYSES OF ROCKS AND MINERALS, 1880-1908. 
L. Diorite dike, near Minnesota mine. Contains quartz, orthoclase, plagioclase, 
hornblende, iron ore, chlorite, and epidote. Analysis by Schaller, No. 2377. 
M. Diorite porphyry, near Uncle Sam mine. Contains quartz, plagioclase, iron ore, 
chlorite, and epidote. Analysis by Schaller, No. 2377. 
N. Diorite dike, near Keswick. Contains hornblende, plagioclase, orthoclase, and 
iron ore. Analysis by Wells, No. 2380. 
O. Diabase, Butcher Creek. Contains plagioclase, orthoclase, pyroxene, horn- 
blende, and iron ore. Analysis by Wells, No. 2380. 
P. Feldspar-epidote rock, dike near Spread Eagle mine. Contains quartz, ortho- 
clase, plagioclase, biotite, epidote, sphene, apatite, and zircon. Analysis by Steiger, 
No. 2378. 
H20 at 105°. . fe eas . 7 4 c -84 
100.09 | 100.39 | 99.67 | 99.91 | 100.06 
In this group of analyses, A to P, when not otherwise stated, TiO, and P, O; were 
not separately determined. 
2, LASSEN PEAK REGION. 
Rocks collected by J. 8. 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 Am. Jour. Sci., 3d ser., vol. 33, p. 49. The analyses are so numerous 
that it seems best to divide them into subordinate groups. 
1. RHYOLITE. 
A. Rhyolite, a short distance northwest of Willow Lake, near the Geyser, Plumas 
County. Alaskose. A light-gray rock with occasional phenocrysts of quartz and 
feldspar in a granular groundmass of the same materials. Analysis by W. F. Hille- 
brand, record No. 414. P. R. C. 1419. 
B. Rhyolite, 2 milesnorthwest of Deer Creek Meadows, Tehama County. Tehamose. 
Shows many small crystals of quartz, feldspar, and biotite in a spherulitic groundmass. 
Analysis by Hillebrand, No. 415. P.R.C. 1420. 
C. Rhyolite, Slate Creek, west of Deer Creek Meadows. Tehamose. Composed 
wholly of spherulites, some of which include crystals of feldspar or biotite. Analysis 
by Hillebrand, No. 416. P. R. C. 1421. 2 
D. Rhyolite, summit of Mount Stover, Plumas County. Toscanose. Composed 
almost wholly of spherulites, with a few crystals of feldspar and hornblende. Analysis 
by Hillebrand, No. 417. P. R. C. 1422. 
E. Rhyolite, near Slate Creek, west of Deer Creek Meadows, Toscanose. A 
pearlite, composed chiefly of little glass balls, with a few spherulites, and crystals of 
feldspar and biotite. Analysis by Hillebrand, No. 418.. P. R. C. 1423. 
