The four following rocks, from Sundance quadrangle, were collected by W. S. Tangier Smith, who has supplied the petrographic data. Analyses by George Steiger, record No. 1999. Hitherto unpublished.

O. Syenite-porphyry. Pulaskose. Contains phenocrysts of orthoclase, ægirine-augite, a little augite, nepheline (?), magnetite, garnet, titanite, and apatite. Groundmass mainly feldspar, probably orthoclase, and other minerals as above, with possibly some species of the sodalite group.

P. Essexite-porphyry. Esserose. Essexose. Contains phenocrysts of feldspar, apparently orthoclase and anorthoclase, ægirine-augite or little augite, garnet, probably nosean, titanite, magnetite, and apatite. In the groundmass, feldspar (orthoclase ?), ægirine-augite, and possibly sodalite.

Q. Syenite-porphyry. Akerose-laurvikose. Contains phenocrysts of feldspar (orthoclase and plagioclase?), ægirine-augite, magnetite, titanite, and apatite. In the groundmass, feldspar, magnetite, ægirineaugite, and apatite.

R. Porphyritic rock. Kentallenose. Contains phenocrysts of augite, magnetite, apatite, biotite, orthoclase, and plagioclase. Same minerals in the groundmass, with perhaps some species of the nepheline-sodalite group.

YELLOWSTONE NATIONAL PARK AND THE ABSAROKA RANGE.

1. ELECTRIC PEAK.

Rocks described by Iddings in 12th Ann., p. 577. Also in Bull. Phil. Soc. Washington, vol. 11, p. 206. For analyses O, P, see Mon. XXXII, Pt. II.

A. Pyroxene-mica-diorite. Tonalose. Contains augite, hypersthene, plagioclase, quartz, biotite, hornblende, magnetite, and apatite. Analysis by J. E. Whitfield, record No. 830. P. R. C. 94.

B. Pyroxene-mica-diorite. Andose. Same minerals as under A. Analysis by Whitfield, No. 921.

C. Pyroxene-mica-diorite. Tonalose. Like A and B. Analysis by W. H. Melville, record No. 1231.

D. Pyroxene-porphyry. Andose. Contains augite, hypersthene, biotite, magnetite, plagioclase, and quartz. Analysis by Whitfield, No. 830.

E. Quartz-pyroxene mica-diorite. Tonulose. Contains biotite, hornblende, augite, hypersthene, magnetite, plagioclase, orthoclase, and quartz. Analysis by Melville, No. 1231.

F. Quartz-mica-diorite. Tonalose. Contains biotite, hornblende, augite, hypersthene, plagioclase, orthoclase, and quartz. Analysis by Whitfield, No. 921.

G. Quartz-mica-diorite. Yellowstonose. Contains biotite, hornblende, plagioclase, pyroxene, quartz, and orthoclase. Analysis by Whitfield, No. 921.

H, I, J. Quartz-mica-diorites. Yellowstonose. Contain hornblende, biotite, plagioclase, orthoclase, and quartz. Analyses by Whitfield, Nos. 921 and 830.

K. Quartz-mica-diorite-porphyry. Yellowstonose. Contains biotite, hornblende, plagioclase, orthoclase, and quartz. Analysis by Whitfield, No. 830.

L. Quartz-mica-diorite-porphyry. Lassenose. Contains quartz, biotite, plagioclase, alkali feldspar, and hornblende. Analysis by Whitfield, No. 830.

M. Hornblende-porphyry. Tonalose. Intrusive sheet. Contains hornblende, plagioclase, magnetite, and quartz. Analysis by Whitfield, No. 429.

N. Hornblende-mica-porphyry. Yellowstonose. Intrusive sheet. Contains hornblende, plagioclase, biotite, magnetite, and quartz. Analysis by Whitfield, No. 420. The Indian Creek laccolith.

O. Augite-andesite-porphyry. Monzonose. Intrusive sheet, upper portion. Contains malacolite, plagioclase, probably orthoclase, magnetite, and little biotite, with secondary chlorite or serpentine and actinolite. Analysis by Whitfield, No. 830.

P. Same sheet as O, lower portion. Kentallenose. Analysis by W. F. Hillebrand, record No. 1571.

2. SEPULCHRE MOUNTAIN.

Rocks described by Iddings, 12th Ann., p. 633. Also in Bull. Phil. Soc. Washington, vol. 11, p. 210, and in Mon. XXXII, Pt. II.

A. Pyroxene-andesite. Tonalose. Essentially composed of augite, hypersthene, and plagioclase. Analysis by J. E. Whitfield, record No. 923.

B. Pyroxene-andesite. Andose. Composition like A. Analysis by Whitfield, No. 923.

C. Hornblende-andesite. Andose. Essentially plagioclase and hornblende. Analysis by Whitfield, No. 922.

D. Hornblende - pyroxene - andesite. Tonalose. Contains augite, hypersthene, plagioclase, and hornblende. Analysis by T. M. Chatard, record No. 712.

E. Hornblende-pyroxene-andesite. Tonalose. Minerals as in D, with magnetite also. Analysis by Chatard, No. 712.