4. CRAZY MOUNTAINS.

The greater number of the rocks in this group were received from J. E. Wolff, who has supplied the petrographic data. The few exceptions are properly indicated. The three tinguaites and the elæolitesyenite were described by Wolff and Tarr in Bull. Mus. Compar. Zoology, vol. 16, No. 12, 1893, in a paper upon Acmite-Trachyte from the Crazy Mountains." The renaming of these rocks is due to Wolff. The analyses, except when otherwise stated, are by W. F. Hillebrand, record No. 1438.

A. Granitite, Big Timber Creek. Toscanose. Small dikes in main diorite stock. Contains quartz, orthoclase, plagioclase (oligoclase), and biotite.

B. Hornblende-granitite, main stock, Big Timber Creek. Dacose. Contains biotite, hornblende, quartz, orthoclase, and plagioclase (oligoclase).

C. Granite-porphyry, intrusive sheet, north part of the mountains. Lassenose. Contains orthoclase, albite, quartz, biotite, and green hornblende in a groundmass of quartz and untwinned feldspar.

D. Porphyrite, intrusive sheet, Sweet Grass Creek. Lassenose. Contains hornblende and andesine in a groundmass of plagioclase, orthoclase, and quartz, with accessory magnetite.

E. Porphyrite, dike in contact zone, Sweet Grass Creek. Toscanose. Contains brown hornblende, biotite, and labradorite in a groundmass of plagioclase, biotite, and hornblende, with a little quartz and orthoclase.

F. Porphyrite, intrusive sheet, middle peak of Three Peaks. Akerose. Contains andesine, hornblende, augite, and biotite in a groundmass of plagioclase, orthoclase, and quartz.

G. Porphyrite, intrusive sheet, north of Shields River Basin. Akerose. Contains plagioclase, hornblende, and biotite, in a groundmass of plagioclase, a little orthoclase, augite, hornblende, and magnetite. H. Porphyrite, intrusive sheet, northern part of the mountains. Akerose. Contains brown hornblende, green augite, and plagioclase, in a groundmass of plagioclase, augite, and magnetite, with accessory apatite.

I. Syenite, ridge north of Shields River Basin. Akerose. Contains hornblende, green augite, and anorthoclase, with accessory sphene, apatite, and magnetite.

J. Diabase-porphyrite (?), dike south of Shields River Basin. I. 5. 3. 4. Contains labradorite and decomposed augite in a groundmass of plagioclase, epidote, and chlorite..

K. Diorite-porphyrite, Big Timber Creek. Andose. Contains labradorite, augite, hornblende, biotite, orthoclase, quartz, magnetite, and apatite.

L. Quartz-diorite, main stock on Sweet Grass Creek. Andose. Contains hornblende, biotite, augite, labradorite, orthoclase, and quartz, with accessory apatite, magnetite, olivine, and hypersthene.

M. Diorite, head of Rock Creek. Shoshonose. Contains biotite, labradorite, and augite, in a groundmass of plagioclase, orthoclase, and quartz, with accessory magnetite, apatite, and hornblende.

N. Diorite, main stock, Big Timber Creek. Andose. Contains biotite, augite, labradorite, quartz, orthoclase, apatite, and magnetite. O. Olivine-gabbro, Big Timber Creek. IV. 2. 1. Contains labradorite (?), brown hornblende, augite, olivine, and magnetite.

P. Rock from Musselshell. River, north of Crazy Mountains. Monchiquose. Received from J. S. Diller, but undescribed. Regarded by W. H. Weed as monchiquite. Analysis by L. G. Eakins, record No. 1021.

Q. Hornstone, metamorphosed shale, contact zone, Sweet Grass Creek. An aggregate of augite, quartz, triclinic feldspar, and biotite.

R. Elæolite-syenite, Peaked Butte, northeast side of the mountains. Umptekose. Described by Wolff and Tarr, loc. cit. Contains anorthoclase, augite, occasionally sodalite, ægirine, apatite, magnetite, and some interstitial nephelite. Analysis by W. H. Melville, record No. 1291. Ra. Anorthoclase from R. Analysis by W. F. Hillebrand, record No. 1297.

S. Tinguaite, var. sölvsbergite, intrusive sheet north of Shields River.

T. Tinguaite, var. sölvsbergite, dike north part of mountains. Nordmarkose.

U. Tinguaite, var. sölvsbergite, dike at head of Sixteenmile Creek. Nordmarkose.

S, T, and U are the rocks described by Wolff and Tarr in their paper upon "Acmite-Trachyte." Mineral composition the same as under R. Analyses by W. H. Melville, record No. 1291.

V. Theralite, Gordons Butte. Malignose. Contains green augite, ægirine, biotite, olivine, nephelite, sodalite, and a feldspar, partly sanidine, containing K, Na, Ba, Sr, and Ca; also accessory apatite, magnetite, and sphene. W. Theralite, Gordons Butte; another sample. Kamerunose. Analysis by E. A. Schneider, record No. 1281. P. R. C. 75. X. Theralite, north of Alabaugh Creek. Wolff for the Educational Series (Bull. 150). biotite, olivine, magnetite, apatite, nephelite of the sodalite group, sanidine, and analcite. Analysis by Schneider, No. 1281. P. R. C. 76.

Esserose. Described by Contains augite, ægirine, partly zeolitized, a mineral

Rocks V, W, and X are described by Wolff in Bull. 150, pp. 197, 199. Y. Altered theralite, head of Shields River, west of Loco Mountain. Received from W. H. Weed. Analysis by H. N. Stokes, record No.

1547.

Z. Hornblende-picrite, Conical Peak. Auvergnose. Data supplied by J. P. Iddings. Contains hornblende, plagioclase, hypersthene, augite, olivine, very little primary quartz, and probably some magnetite and apatite. Analysis by L. G. Eakins, record No. 1379.

Rocks collected by W. H. Weed and L. V. Pirsson. Described in a paper on the Neihart and Barker mining districts in Pt. III of the 20th Ann. Analyses by W. F. Hillebrand, record No. 1476, and H. N. Stokes, record No. 1547.

A. Quartz-porphyry, Yogo Peak, sheet at head of Belt and Running Wolf creeks. Toscanose. Phenocrysts of orthoclase and quartz in a groundmass of quartz and alkali feldspar, with a little white mica and some kaolin. Chlorite, limonite, and calcite are also present, pseudomorphous after biotite and perhaps hornblende. Total amount of secondary minerals very small. Analysis by Hillebrand.