2. BUTTE DISTRICT.

Rocks received from W. H. Weed and G. W. Tower. Some of the granite rocks are described by Weed in Journ. Geol., vol. 7, p. 737. All the rocks are to be described in a forthcoming monograph on Butte.

A. Butte granite. Amiatose. A quartz-monzonite, variety banatite, from Walkerville Station. Contains quartz, andesine, orthoclase, hornblende, and biotite, with a little titanite, apatite, and magnetite. B. Biotite from A.

C. Amphibole from A.

Analyses A, B, C, by H. N. Stokes, record Nos. 1686, 1808.
D. Butte granite, Gagnon mine, Butte.

Amiatose.
Harzose.

E. Butte granite, Atlantic mine, Butte. F. Butte granite, Alice mine, Butte. Harzose. Analyses D, E, and F, by W. F. Hillebrand, record No. 1692. Mineralogically the rocks are like A and D.

The six following analyses represent alterations of quartz-monzonite, the so-called Butte granite:

G. Weathered Butte granite.

H. Altered Butte granite. Decomposed near quartz-pyrite veins. Shows opaline silica, with sericite derived from feldspar. Hornblende gone; mica recognizable only as sericite masses having the form of biotite.

Analyses G and H by Stokes, record Nos. 1792, 1787.

I. Altered Butte granite, 300-foot level, Colusa mine. Derived from A. Contains quartz, altered orthoclase and plagioclase, and sericite.

J. Altered Butte granite, wall rock, 1,300-foot level, Parrot mine. Derived from A. Contains quartz, sericite, pyrite, bornite, etc.

K. Altered Butte granite, enargite vein, 1,000-foot level, Leonard mine. Contains quartz, kaolin, pyrite, etc.

L. Altered Butte granite, veinlets in Original mine. Contains quartz, sericite, partly altered feldspars, calcite, zinc blende, etc. Analyses I, J, by E. T. Allen, record No. 1964; K, L, by W. F. Hillebrand, record No. 1971.

M. Bluebird granite, Nettie mine. orthoclase and quartz, with a little biotite. Analysis by H. N. Stokes, N. Same rock and locality as M. record No. 1692.

Alaskose. An aplite. Contains plagioclase and a sprinkling of record No. 1686.

Analysis by W. F. Hillebrand,

O. Pitchstone, or rhyolite-dacite obsidian, Butte. Lassenose. Phencerysts of andesine, quartz, and orthoclase in a glassy base. P. Rhyolite, Hyde Park dike. Tehamose. Contains sanidine, quartz, plagioclase, and biotite in a groundmass of quartz and feldspar. Analyses O, P, by Stokes, record No. 1686.

Q. Quartz porphyry, Modoc mine. Toscanose. Contains quartz, orthoclase, and plagioclase in a groundmass of quartz and feldspar. A few small biotites are present. Feldspar partly altered to sericite. Analysis by Hillebrand, record No. 1692.

R. Altered rhyolite-porphyry, 1,800-foot level, Anaconda mine. Contains quartz phenocrysts, with sericite, pyrite, etc. Analysis by Hillebrand, record No. 1971, partial only.

3. BOULDER BATHOLITH.

Rocks collected by W. H. Weed, who supplies the petrographic data.

A. Quartz-monzonite, or "Butte granite," from the Frohner mine, 10 miles south of Helena. Harzose. Contains quartz, andesine, orthoclase, hornblende, and biotite, with minor accessories.

B. Granite, Boulder type, near Boulder. Near adamellite. Toscanose. Contains quartz, feldspar, black mica, and dark-green hornblende. Has an unusual amount of plagioclase.

C. Diorite, Red Mountain. Andose. Contains pale-green to colorless hornblende, plagioclase varying from labradorite to albite, some orthoclase, and a little quartz. Biotite, apatite, and magnetite also

occur.

D. Diorite, Red Mountain. Kentallenose. Contact of granite with limestones. Consists mainly of green hornblende and "basic" plagioclase. Little quartz present.

E. Quartz-monzonite, Red Rock Creek. Harzose. Contains hornblende, augite, biotite, plagioclase, and orthoclase, with a little magnetite and apatite.

Analyses by H. N. Stokes, record Nos. 1686, 1787.

F. Rhyolite, top of Red Mountain, Rimini. Liparose. Quartz and feldspar phenocrysts in a groundmass of the same minerals.

G. Andesite-porphyry, Hiawatha Creek, above basin. Amiatose. Contains plagioclase, orthoclase, and augite.

H. Andesite-porphyry, Zosel mining district, near Daylight. Near bandose. Somewhat altered. Contains augite, andesine, and olivine in a groundmass of plagioclase, augite, and iron oxide. Ferromagnesian minerals altered to serpentine. Analyses by H. N. Stokes, record Nos. 1686, 1787.