9. BEARPAW MOUNTAINS.

Described by Weed and Pirsson, Amer. Journ. Sci., 4th series, vol. 1, pp. 283 and 351, and vol. 2, pp. 136 and 188. Analyses by H. N. Stokes, record Nos. 1558 and 1572.

Nordmarkose. Con

A. Quartz-syenite-porphyry, Gray Butte. tains anorthoclase, microlites of plagioclase, ægirite, augite, quartz, and apatite, with an occasional zircon and very few biotite leaves. P. R. C. 897.

B. Quartz-syenite, Beaver Creek stock. Liparose. Contains orthoclase, albite, quartz, augite, and iron oxides, with very little biotite hornblende, and sphene. P. R. C. 900.

C. Basic syenite or monzonite (yogoite), Beaver Creek. Monzonose. Contains orthoclase, plagioclase, diopside, biotite, iron oxides, and apatite. P. R. C. 902.

D. Shonkinite, Beaver Creek. SR. 3 of wyomingase. Contains anorthoclase, diopside, biotite, iron oxides, and apatite, with very little olivine and probably a trace of nephelite. P. R. C. 901.

E. Leucitite, Bearpaw Mountains. Chotose. An olivine-free leucitebasalt. Contains leucite, augite, iron oxides, rarely biotite, and very little glassy base. P. R. C. 903.

F. Tinguaite, dike on Bear Creek. Judithose. Contains orthoclase, nephelite, cancrinite, augite, ægirite, apatite, a little sodalite, and a doubtful fibrous hornblende. P. R. C. 899.

G. Pseudo-leucite-sodalite-tinguaite. Beaver Creek. Janeirose. Contains orthoclase, nephelite, sodalite, nosean, ægirite. diopside, and fluorite. P. R. C. 904.

10. ELKHORN MINING DISTRICT.

Rocks collected by W. H. Weed. rell in 22d Ann., Part II, p. 511. No. 1858.

Described in detail by J. S. BarAnalyses by H. N. Stokes, record

A. Gabbro, west side of Black Butte. Hessose. Contains labradorite, augite, hornblende, biotite, and magnetite, with a little quartz and zircon. P. R. C. 351.

B. Andesite, Elkhorn Mountain. Adamellose. Contains plagioclase, hornblende, biotite, and pyroxene. P. R. C. 413.

C. Hornblende-andesite porphyry, southwestern part of the district. Contains plagioclase and hornblende phenocrysts in a groundmass of hornblende. Pyrite, pyrrhotite, and perhaps magnetite are also present. P. R. C. 412.

D. Quartz-monzonite, Elkhorn. Harzose. Contains labradorite, orthoclase, quartz, biotite, hornblende, augite, magnetite, apatite, and titanite. P. R. C. 407.

E. Aplite, north of Black Butte, middle of intrusion. tehamose. P. R. C. 410.

Toscanose

E and F contain soda

F. Like E, eastern side of intrusion. orthoclase and quartz, with a little plagioclase and occasional crystals

of magnetite and biotite. P. R. C. 411.

11. BITTERROOT RANGE.

Quartz-monzonite, near head of Mill Creek. Toscanose. To be described by Lindgren in a forthcoming professional paper. Analysis by W. F. Hillebrand, record No. 1921. Contains quartz, potash feldspar, plagioclase, biotite, apatite, titanite, and magnetite.

Rocks described by Joseph Barrell, but descriptions hitherto unpublished. Analyses by George Steiger, record No. 2021.

A. Hornblende-mica-diorite, near West Belmont mine, east slope of Mount Belmont. Andose-shoshonose. Contains feldspars, 60 per cent; hornblende, 35 per cent; and small amounts of quartz, magnetite, biotite, augite, and apatite.

B. Hornblende-porphyrite, north slope of the town of Bald Butte. Andose. Contains feldspar, largely oligoclase, about 75 per cent; and hornblende, 23 per cent; with secondary hornblende, calcite and chlorite.

C. Quartz-diorite, road up Woodchopper Gulch. Tonalose. Typical of the Marysville batholith. Contains andesine, 52 per cent; quartz, 31 per cent; orthoclase, 11 per cent; and minor biotite, hornblende, magnetite, titanite, and apatite.

IDAHO.

Rocks A to K, inclusive, are described by Waldemar Lindgren in 20th Ann., Part III, p. 75.

A. Quartz-monzonite, Idaho-Democrat mine, Hailey. Toscanose. Contains quartz, orthoclase, microcline, oligoclase, biotite, apatite, titanite, and magnetite. Sp. gr., 2.672, 27.5°.

B. Same rock and locality as A, but in altered condition. Contains quartz, sericite, chlorite, calcite, pyrite, rutile, etc. Sp. gr. 2.472, 29°. C. Diorite, Croesus mine, Hailey. Andose. Andose. Contains labradorite, biotite, diallage, hypersthene, hornblende, quartz, titanite, magnetite, orthoclase, and chlorite. Sp. gr., 2.826, 28°.

D. Same rock and locality as C, but in altered condition. Contains quartz, sericite, chlorite, calcite, pyrite, arsenopyrite, rutile, etc. Sp. gr., 2.898, 28°.

Analyses A to D by W. F. Hillebrand, record No. 1826. The metals which are bracketed with sulphur represent sulphides. Traces of lithia are present in all four.