4. BUTTE COUNTY.

Rocks from this county are also to be found under the heading of the Lassen Peak region. The following rocks were collected by H. W. Turner, to whom the petrographic data are due. Analyses, with two exceptions, by W. F. Hillebrand, record Nos. 1432, 1456, 1461, and 1548. Analysis G is by H. N. Stokes, record No. 1562.

A. Granodiorite, north side of south fork of Feather River, opposite Enterprise. Described in 14th Ann., p. 441. Contains plagioclase, potash feldspar, quartz, hornblende, brown mica, and accessory minerals. The ferromagnesian minerals are largely altered to chlorite. P. R. C. 720.

B. Granodiorite, 2 miles east of Bangor. Composition like A. The mica is largely altered to chlorite. See 14th Ann., p. 441. P. R. C. 717. C. Diorite, South Honcut Creek. Description supplied by Turner. Contains feldspar, probably all plagioclase, brown hornblende, and a little chlorite. P. R. C. 775.

D. Quartz-diorite, 4.6 miles south of Table Mountáin, on ridge between Butte and Plumas counties. Described in 17th Ann., Part I, p. 521. Contains hornblende, feldspar, quartz, rutile, and a little secondary chlorite and epidote. P. R. C. 758.

E. Amphibole separated from E. Analysis by William Valentine. record No. 1723. Cr2O, determination by Hillebrand.

Contains

F. Meta-andesite-tuff. Described in 14th Ann., p. 441. plagioclase, augite, epidote, chlorite, and secondary hornblende. P. R. C. 719.

G. Uralite-diorite, 1 mile southeast of Forbestown. Described in 17th Ann., Part I, p. 521. Contains plagioclase, hornblende, and magnetite. P. R. C. 751.

H. Basalt, Oroville, Table Mountain. Described in 14th Ann., p. 441. Contains plagioclase, olivine, augite, and magnetite. P. R. C.

718.

I. Altered peridotite, 5 miles northeast of Strawberry Valley. Largely serpentine, with olivine, hornblende, magnetite, and calcite or dolomite. P. R. C. 742.

5. SIERRA COUNTY.

Rocks collected and described by H. W. Turner. See paper in 17th Ann., Part I, p. 521. Additional details, supplied by Turner, are given here. Analyses A to H by W. F. Hillebrand, record Nos. 1456 and 1548. Analysis I by H. N. Stokes, record No. 1514.

A. Granulite (aplite), Yuba Gap, road east of Sierra Buttes. Contains orthoclase, microcline, quartz, plagioclase, some shreds of greenish mica, and a little iron ore, chlorite, and apatite. P. R. C. 730. B. Granulite (aplite), dike east of Milton. Contains orthoclase, quartz, plagioclase, a little microcline, brown mica, and iron ore. P. R. C. 734.

C. Biotite-quartz-monzonite, Indian Valley. Contains plagioclase, orthoclase, quartz, brown mica, apatite, and iron ore. P. R. C. 737. D. Quartz-diorite-porphyry, dike in Indian Valley granite. Contains plagioclase, hornblende, biotite, and quartz. P. R. C. 738.

E. Quartz-mica-diorite, large area east of Milton. Contains plagioclase, a turbid feldspar which is apparently not orthoclase, quartz, green hornblende, brown mica, iron ore, and apatite. P. R. C. 732.

F. Diabase-porphyry, dike east of Milton. Contains labradorite and other plagioclase, augite, and hornblende, the last mineral being perhaps secondary. P. R. C. 733.

G. Hypersthene-andesite, point northeast of Goodyears Bar. Contains plagioclase and rhombic pyroxene, a little augite, and scales which seem to represent former biotite, now replaced by magnetite. P. R. C. 731.

H. Hornblende-pyroxene-andesite, dike southeast of Poker Flat. Contains plagioclase, augite, hornblende, magnetite, some glass, and occasional quartz. P. R. C. 736.

I. Quartz-bearing andesite, northwest of Downieville. Contains plagioclase, augite, enstatite, magnetite, occasional quartz, and probably glass. P. R. C. 753.

6. NEVADA CITY AND GRASS VALLEY.

Rocks of a mining district in Nevada County, described by Lindgren in 17th Ann., Part II, p. 1.

A. Granodiorite, 1 mile southeast of Nevada City. Contains hornblende, biotite, quartz, plagioclase, orthoclase, magnetite, apatite, sphene, and pyrite. Analysis by W. F. Hillebrand, record No. 1478.

B. Granodiorite, Kate Hayes Hill, Grass Valley. Contains plagioclase, orthoclase, quartz, hornblende, pyrite, magnetite, apatite, sphene, and zircon. Analysis by Hillebrand, No. 1478.

C. Hornblende-porphyrite, Nevada City. Contains feldspar, hornblende, quartz, epidote, sericite, and biotite. Analysis by H. N. Stokes, record No. 1531.

D. Quartz-porphyrite, New Ophir claim, Grass Valley. Contains plagioclase, quartz, uralite, epidote, and augite, and hornblende altered into chlorite. Analysis by Stokes, No. 1531.

E. Diabase, near Maryland mine, Grass Valley. Contains feldspar, augite, hornblende, ilmenite, pyrrhotite, pyrite, and some chlorite. Analysis by Stokes, No. 1522.

F. Diabase, Grass Valley. Contains feldspar, pyroxene, hornblende, ilmenite, pyrrhotite, pyrite, and chlorite, and probably a little quartz. Analysis by Stokes, No. 1522.