L. Garnetiferous gabbro, Granite Falls. Bandose. Described by W. S. Bayley in Bull. 150, p. 282. Contains plagioclase, augite, garnet, magnetite, a little hornblende, some quartz grains, and apatite. Analysis by H. N. Stokes, record No. 1296. Sp. gr., 3.105. P. R. C. 109.

M. Gabbro-diorite, Minnesota Falls. Iessose. Described by Bayley in Bull. 150, p. 369. Essentially plagioclase and hornblende, with some kaolin, augite, and biotite. Analysis by Stokes, No. 1296. Sp. gr., 2.935. P. R. C. 144.

N. Quartz-norite-gneiss, Odessa. Described by Bayley in Bull. 150, p. 358. Contains quartz, plagioclase, pyroxene, biotite, garnet, magnetite, and sulphide of iron. Analysis by Stokes, No. 1296. Sp. gr., 2.770. P. R. C. 140.

O. Mica-schist, bed of Cross River, near Gunflint Lake. Description furnished by C. R. Van Hise. Contains biotite, quartz, feldspar (?), and pyrites. Analysis by T. M. Chatard, record No. 896.

P. Actinolite-magnetite-schist, SE. 4 of SE. 4 of sec. 34, T. 61 N., R. 12 W. Described by Bayley in Amer. Journ. Sci., 3d series, vol. 46, p. 178. Mainly actinolite and magnetite. Analysis by W. H. Melville, record No. 1403.

Q. Magnetite rock near the preceding, also described with P by Bayley. Analysis by Melville, No. 1403.

SOUTH DAKOTA.

A. Phonolite, Black Hills. Miaskose. Described by Whitman Cross in Bull. 150, p. 191. Contains sanidine, nephelite, ægirite, nosean, and sodalite, with accessory sphene, apatite, and zircon, and possibly some rare zirconates or titanates. Also, sparingly, secondary zeolites and calcite. No magnetite, but minute ferritic flakes are disseminated through the rock. Analysis by W. F. Hillebrand, record No. 1618. P. R. C. 73.

B. An earlier analysis of A, by H. N. Stokes, record No. 1314. This was made along the ordinary lines as regards "completeness," as requested by the collector, and without regard to minor accessory constituents. It serves well to illustrate the difference between the two modes of treatment, in comparison with the fuller analysis.

C. Tourmaline-biotite-schist, north of Harney Peak, Black Hills. Described by Bayley in Bull. 150, p. 327. Contains quartz, biotite, tourmaline, a little garnet and rarely muscovite, iron ore, and apatite. Analysis by Stokes, record No. 1296. P. R. C. 130.

D. Volcanic ash, 3 miles west of Argyle, Custer County. Amiatose. Collected by N. H. Darton. Analysis by George Steiger, record No. 1875.

WYOMING.

Rocks A to J, inclusive, studied by Whitman Cross. The Leucite Hills series is described in Amer. Jour. Sci., 4th ser., vol. 4, p. 115. Analysis J is by L. G. Eakins, record No. 1078. The others are by W. F. Hillebrand, one made in the Denver laboratory, and record Nos. 343, 355, 362, 368, 403, 463, 1668, and 1682.

A. Wyomingite, Boars Tusk, Leucite Hills.

Wyomingose. Contains phlogopite, leucite, diopside, and apatite. Sp. gr., 2.779, 13.5°. P. R. C. 567.

B. Wyomingite, Fifteenmile Spring, Leucite Hills. Composition like A. Sp. gr., 2.627, 30°. P. R. C. 566.

C. Portion of B soluble in 2.5 per cent nitric acid.

D. Phlogopite from wyomingite.

Orendose.

Contains

E. Madupite, Pilot Butte, Leucite Hills. Madupose. predominating diopside and phlogopite, with perofskite and magnetite, in a glassy base which has approximately the composition of leucite. Sp. gr., 2.857, 22°. P. R. C. 576.

Orendose.

Con

F. Orendite, Fifteenmile Spring, Leucite Hills. tains predominating leucite and sanidine, with phlogopite, a little biotite, diopside, and amphibole, and accessory apatite and rutile. Sp. gr., 2.686, 23.5°. P. R. C. 72 and 572.

G. Orendite, North Table Butte, Leucite Hills. Orendose. Composition like F. Sp. gr., 2.699, 19°. P. R. C. 570.

H. Groundmass of F. Sp. gr., 2.615, 19°. Not cited in published paper.

I. Diopside separated from mixed wyomingite and madupite. Sp. gr., 3.290, 20 ̊. Analyzed in the Denver laboratory. P2O, included with TiO..

5

J. Dacite?, Garfield Peak. Phenocrysts of plagioclase and hornblende, with microscopic sphene and apatite in a groundmass containing plagioclase, orthoclase, quartz, and magnetite. Sp. gr., 2.576, 26.2°. P. R. C. 159.

The four following rocks were collected by A. C. Spencer in Encampment quadrangle. Petrographie data supplied by Spencer. Analyses by E. T. Allen, record No. 2048.

K. Norite, near head of Cow Creek, about three-fourths of a mile from Bridger Peak. Auvergnose. Contains chiefly hypersthene and labradorite, the latter slightly altered to sericite. Biotite and magnetite are present, with a few grains of diallage and a little hornblende. L. Diorite derived from norite, altered form of K. The pyroxene is completely changed to uralite, and the feldspar is largely decomposed.

M. Diorite derived from norite, 2 miles west of the Verdi mine. Contains uralite and labradorite, with a little biotite and magnetite. N. Diorite, probably derived from gabbro, near head of Big Sandstone Creek. Contains much zoisite derived from the feldspars.