J. Porphyritic lamprophyre, allied to camptonite, Indian Trail Ridge, La Plata quadrangle. Camptonose. Contains phenocrysts of green hornblende and colorless diopside in a subordinate groundmass of plagioclase, orthoclase (?), augite, magnetite, and apatite. Much secondary calcite and some serpentine. Analysis by W. F. Hillebrand, record No. 1640. Sp. gr., 2.912, 19.5. P. R. C. 1288. K. Lamprophyre, allied to camptonite, Black Face, Telluride quadrangle. Andose. Consists of a fine felt of plagioclase, augite, and brown hornblende microlites, with flakes of biotite, and a cryptocrystalline part, which is probably in large degree orthoclase. Some magnetite and apatite. Analysis by Hillebrand, record No. 1719. Sp. gr., 2.783, 22. P. R. C. 1282.

L. Quartz monzonite, northeast of San Miguel Peak, Telluride quadrangle. Toscanose. Contains orthoclase and plagioclase in about equal amounts, with abundant quartz and much less augite, horn. blende, biotite, magnetite, and apatite. Analysis by H. N. Stokes, record No. 1764. Sp. gr., 2.720, 34°. Described by Cross in 21st Ann., part 2. P. R. C. 1279.

M. Gabbroitic facies of a diorite-monzonite stock, Ophir Needles, Telluride quadrangle. Tomalose. Contains abundant labradorite, with augite, hypersthene, biotite, orthoclase, magnetite, apatite, and a very little quartz. Analysis by Stokes, record No. 1764. Sp. gr., 2.860, 33°.

N. Gabbro-porphyry, pass south of Mount Sneffels, Telluride quadrangle. Andose. Contains numerous phenocrysts of labradorite or bytownite, in a groundmass of plagioclase, orthoclase (?), augite, hypersthene, biotite, magnetite, and apatite. Analysis by Stokes, record No. 1764. Sp. gr., 2.949, 26.5°. P. R. C. 1280.

O. Rhyolite vitrophyre, ridge east of Windy Gap, Telluride quadrangle. Yellowstonose-lassenose. P. R. C. 1281. Analysis by H. N. Stokes.

Rocks P to T, from the Silverton quadrangle, are described by F. L. Ransome in Bull. 182.

P. Altered andesitic breccia, White Cloud mine. Contains quartz, kaolin, pyrite, rutile, and some undeterminable minerals. Analysis by George Steiger, record No. 1886.

Q. Latite, country rock, Polar Star mine, Engineer Mountain. SR. 3 of vaalase. Contains labradorite, orthoclase (?), quartz, diopside, chlorite, calcite, serpentine, kaolin, magnetite, hematite, apatite, rutile, and leucoxene. Mainly feldspar and quartz.

R. Altered latite, same locality as P, wall rock of vein. Contains mainly quartz and kaolin, with diaspore, pyrite, sericite, rutile, and apatite.

Adamellose.

S. Monzonitic porphyry, near Yankee Girl mine. Contains albite, quartz, orthoclase, chlorite, calcite, sericite, iron ores, pyrite, and apatite.

T. Altered monzonitic porphyry, near National Belle mine. Contains quartz, kaolin, pyrite, diaspore, sericite, apatite, and rutile. Analyses Q to T by H. N. Stokes, record No. 1888.

Rocks U to X, also from Silverton quadrangle, were collected by Whitman Cross, who supplies the petrographic data. Analyses, hitherto unpublished, by W. F. Hillebrand, record Nos. 2024, 2042, 2045. U. Quartz-latite, ridge north of Pole Creek. Amiatose near yel lowstonose. Contains phenocrysts of andesine, hornblende, and a little biotite, in a predominant groundmass of orthoclase, plagioclase, quartz, and a little augite, biotite, and magnetite. P. R. C. 1353.

V. Quartz-latite, bench south of Greenhalgh Mountain. Toscanose. Contains phenocrysts of oligoclase-andesine and biotite in a groundmass of orthoclase, quartz, and rare accessories. P. R. C. 1354. W. Pyroxene-andesite, ridge west from Edith Mountain.

ose.

Tonal

Contains phenocrysts of labradorite, augite, hypersthene, biotite, and magnetite, in a groundmass which is largely glass, with feldspar microlites and ferritic particles. P. R. C. 1355.

X. Pyroxene-andesite, Dolly Varden mine, Henson Creek. Harzose. Contains phenocrysts of labradorite, hypersthene, augite, and magnetite, in a groundmass of plagioclase, orthoclase, quartz, augite, magnetite, etc. P. R. C. 1356.

10. MISCELLANEOUS ROCKS.

A. Rhyolite, east bank of Arkansas River, Nathrop. Liparose. Described by Cross in Proc. Colorado Sci. Soc., vol. 2, p. 69. Contains quartz and sanidine in a groundmass mainly of quartz and alkali feldspar. This rock carries topaz and spessartite in its lithophysae. Analysis made by L. G. Eakins in the Denver laboratory. Sp. gr., 2.602, 29°. P. R. C. 598.

B. Granite, Platte Canyon. Alaskose. Described by E. B. Mathews in Bull. 150, p. 172. Contains microcline, quartz, biotite, oligoclase, and fluorite. Apatite, zircon, magnetite, hematite, limonite, epidote, and rutile (?) are sometimes present. Analysis by H. N. Stokes, record No. 1314.

senose.

C. Hornblende-porphyrite, Hermano Peak, Sierra El Late. LasDescribed by Cross in 14th Ann., p. 165. Contains plagioclase, hornblende, rare quartz, and a little biotite. Analysis by W. F. Hillebrand, record No. 1429.

Tonalose.

D. Hornblende-porphyrite, Ute Peak, Sierra El Late. Described by Cross in 14th Ann., p. 165. Contains plagioclase, hornblende, and very little augite, in a groundmass of quartz, orthoclase, and plagioclase. Analysis by Hillebrand, No. 1429.

E. Porphyritic augite-diorite, Lone Cone, San Miguel Mountains. Tonalose. Described by Cross in 14th Ann., p. 165. Contains plagioclase, augite, hornblende, and biotite, in a groundmass of quartz, orthoclase, and plagioclase. Inclusions of magnetite and apatite in the augite. Analysis by Hillebrand, No. 1429.

F. Tinguaite?, Two Buttes. Laurdalose. Collected by G. K. Gilbert; petrographic data supplied by Whitman Cross. Consists chiefly of pale-green augite, hornblende, apatite, magnetite, and occasional crystals of alkali feldspar, in an obscure, largely isotropic groundmass. Sp. gr., 2.79, 25°. P. R. C. 1393.

G. Pyroxene from F. Sp. gr., 3.43, 28°.
H. Portion of F soluble in nitric acid.

I. Syenitic lamprophyre?, Two Buttes. Prowersose. Collected by Gilbert; description by Cross. Chief constituents, diopside, alkali feldspar, considerable biotite, magnetite, and olivine. The ferromag nesian minerals predominate. Sp. gr., 2.88, 29°. P. R. C. 1394. J. Pyroxene from I. Sp. gr., 3.45, 25°.

Analyses F to K by W. F. Hillebrand, record No. 1604.