MONTANA.

1. MADISON AND GALLATIN VALLEYS.

Rocks collected by A. C. Peale and G. P. Merrill. Described by Merrill in Proc. U. S. National Museum, vol. 17, p. 637. See also Bull. 110, p. 47.

A. Basalt?, east side of Bozeman Creek, 24 miles southeast of Bozeman. Kentallenose. Contains olivine and augite, chloritized and serpentinized. The colorless groundmass contains apparently two feldspars and a pyroxene, with grains of iron oxide. Analysis by T. M. Chatard, record No. 517. Sp. gr., 2.86. P. R. C. 971.

B. Pyroxene from A. Analysis by L. G. Eakins, record No. 1046. C. Portion of A soluble in hydrochloric acid. Contains olivine, iron oxides, and decomposition products. Analysis by Eakins, record No. 817.

D. Highly altered porphyrite?, hills 1 mile north of East Gallatin River, near Camp No. 6. Rock contains hornblende paramorphs after augite in a devitrified base, with amygdules of calcite, chloritic and ferruginous matter derived from porphyritic augite and olivine. The base is also filled with needles, which may be mica. Analysis by Eakins, record No. 820. P. R. C. 968.

E. Lamprophyre, Cottonwood Creek. Monzonose. Contains porphyritic augite and olivine in an indeterminate groundmass carrying augite, iron oxides, and mica. Analysis by Chatard, record No. 516. P. R. C. 979.

F. Augite-porphyry, Cottonwood Creek. Shoshonose. Contains feldspars, augite, and brown mica, with iron oxides, apatite, glass, and secondary calcite and chlorite. Carries porphyritic plagioclase and augite. No unaltered olivine visible. Sp. gr., 2.785. Analysis by Eakins, record No. 819. P. R. C. 965.

G. Basalt?, Bear Creek. Lamarose. Resembles A, but with a more crystalline groundmass. Contains plagioclase, possibly sanidine, augite, olivine, and iron oxides. Analysis by Chatard, record No. 1154. P. R. C. 967.

H. Lamprophyre, between South Boulder and Antelope creeks. Kentallenose. Contains porphyritic augite and olivine in a feldspathic groundmass, with apatite, augite, grains of iron oxide, and shreds of brown mica. Sp. gr., 2.96. Analysis by Eakins, record No. 1266. P. R. C. 966.

I. Lamprophyre, hills east of South Boulder Creek. Near auvergnose. Nodules from a decomposed mass. Shows sanidine, plagioclase, brown mica, and altered olivine.

J. Hornblende-picrite, North Meadow Creek. Wehrlose. Contains hornblende, abundant fresh olivine, grains of pleonaste and iron oxides, and occasionally hypersthene. Sp. gr., 3.35. P. R. C. 973. K. Pyroxenite, divide between Meadow and Granite creeks. Contains hornblende and hypersthene, with grains of iron oxide. P. R. C. 972.

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Cook

L. Hypersthene-andesite, northwest of Red Bluff. Tonalose. Contains plagioclase and pyroxene, with an amorphous glassy base, and sometimes olivine altered to chloritic matter.

M. Peridotite, var. wehrlite, hills 3 miles northwest of Red Bluff. Wehrlose. Contains olivine, diallage, brown mica, rarely plagioclase, and secondary iron oxides. Sp. gr., 3.37. Analyses J, K, L, and M by Eakins, record No. 1266. P. R. C. 975 and 976.

The following rocks, at first supposed to be Pliocene sandstones, were also described by Merrill, Amer. Journ. Sci., 3d series, vol. 32, p. 119. All consist of pumiceous volcanic glass. C, from Idaho, is included here for convenience. Analyses by J. E. Whitfield, record No. 382. A. Little Sage Creek.

B. Devils Pathway.

C. Marsh Creek Valley, Idaho.

Iron and alumina weighed together. The iron is mostly in the ferrous form.

The following examples of volcanic dust or sand, from the Gallatin Valley, were collected by A. C. Peale. Analyses A, B, C, and D by F. W. Clarke, record No. 379. Analysis E by H. N. Stokes, record No. 1314.

A. Dry Creek Valley, above the mouth of Pass Creek.

B, C. Near Bozeman.

D. Near Fort Ellis.

E. Essentially rhyolitic glass, described by Iddings in Bull. 150, p. Gallatin Valley. P. R. C. 58.

146.