2. ROCKS FROM EUREKA.

Described by Hague and Iddings, Mon. XX.

A. Basalt, summit of Richmond Mountain. Red, porous. Contains augite, less hypersthene, feldspars, and magnetite, in a glassy base, with accessory olivine and quartz. Analysis by J. E. Whitfield, record No. 424.

B. Andesitic perlite, south of Carbon Ridge. Contains plagioclase, hornblende, biotite, quartz, hypersthene, augite, magnetite, apatite, and zircon, with a glassy base. Analysis by W. H. Melville, record No. 1240.

CALIFORNIA.

1. MOUNT SHASTA.

Description of rocks furnished by J. S. Diller, who also describes A, B, and C in Bull. 150, pp. 221, 227.

A. Hornblende-andesite, Black Butte, west base of Shasta. Contains plagioclase and hornblende in a microlitic groundmass. The latter carries hypersthene, magnetite, and amorphous matter. Analysis by W. H. Melville, record No. 1346. P. R. C. 84.

B. Hypersthene-andesite, older flow, west base of Shasta. Contains plagioclase, hypersthene, magnetite, and glass. Analysis by Melville, No. 1346.

C. Hypersthene-andesite, like B, same locality, later flow. Analysis by Melville, No. 1346. P. R. C. 87.

D. Hornblende-andesite, late flow, eastern side of Shasta. Contains small crystals of plagioclase and hornblende in a dark groundmass. Thin section not examined. Analysis by H. N. Stokes, record No. 1532. E. Ophitic basalt from near the McCloud River, south of Mount Shasta. A gray cellular rock. Thin section not examined. Analysis by Stokes, No. 1532.

F. Andesite basalt, Delta, Shasta County. Much plagioclase and a few hypersthene crystals in a groundmass chiefly of feldspar, pyroxene, magnetite, and trace of olivine. Analysis by Melville, No. 1346.

The following rocks are from Shasta County, but not within either the Mount Shasta or the Lassen Peak areas. Collected by J. S. Diller, who furnishes the petrographic data.

A. Dacite-porphyry, east fork of Clear Creek, 9 miles above French Gulch. Contains conspicuous phenocrysts of plagioclase, a few of quartz, and smaller ones of biotite and pyroxene, in a groundmass of quartz and feldspar. Analysis by J. E. Whitfield, record No. 970.

B. Dacite-porphyry, Smiths Gulch, 6 miles up Clear Creek from French Gulch. Contains phenocrysts of plagioclase, quartz, biotite, and hornblende, in a groundmass chiefly of quartz and feldspar. Analysis by Whitfield, No. 971. Also described by J. P. Iddings in Bull. 150, p. 233. P. R. C. 90.

C. Diorite, from Ono. Not described. Analysis by T. M. Chatard, record No. 1107.

Rocks collected by J. S. Diller, who has furnished the petrographic data. Nearly all are from the area covered by the Lassen Peak atlas sheet of the U. S. Geological Survey. The quartz basalts have been described by Diller in Bull. 79, and partly in Amer. Journ. Sci., 3d series, vol. 33, p. 49. The analyses are so numerous that it seems best to divide them into subordinate groups.

1ST. RHYOLITES.

A. Rhyolite, a short distance northwest of Willow Lake, near the Geyser, Plumas County. A light-gray rock with occasional phenocrysts of quartz and feldspar in a granular groundmass of the same materials. Analysis by W. F. Hillebrand, record No. 414.

B. Rhyolite, 2 miles northwest of Deer Creek Meadows, Tehama County. Shows many small crystals of quartz, feldspar, and biotite in a spherulitic groundmass. Analysis by Hillebrand, No. 415.

C. Rhyolite, Slate Creek, west of Deer Creek Meadows. Composed wholly of spherulites, some of which include crystals of feldspar or biotite. Analysis by Hillebrand, No. 416.

D. Rhyolite, summit of Mount Stover, Plumas County. Composed almost wholly of spherulites, with a few crystals of feldspar and hornblende. Analysis by Hillebrand, No. 417.

E. Rhyolite, near Slate Creek, west of Deer Creek Meadows. A pearlite, composed chiefly of little glass balls, with a few spherulites, and crystals of feldspar and biotite. Analysis by Hillebrand, No. 418.

F. Rhyolite, 1 miles northeast of Clipper Mills, on tramway to Rock Creek, Shasta County. A spherulitic rock containing a few microscopic particles of feldspar and hornblende. Analysis by Hillebrand, No. 678.

G. Rhyolite-tuff, divide between the west fork of Willards Creek and the stage road, in Lassen County. Elevation, 5,800 feet. Composed almost wholly of fine angular particles of clear glass. Analysis by George Steiger, record No. 1427.

Materials for A to F dried at 110° previous to analysis.

2D DACITES AND ANDESITES.

A. Gray dacite, Lassen Peak. Contains hornblende, biotite, plagioclase, quartz, scarce pyroxene, magnetite, apatite, and a glassy base. Analysis by T. M. Chatard, record No. 111. P. R. C. 82.

B. Secretion in dacite, Lassen Peak. Composed chiefly of plagioclase and hornblende. Analysis by Chatard, No. 110.

C. Reddish dacite, Lassen Peak. Chatard, No. 110. P. R. C. 82.

Essentially like A. Analysis by

D. Dacite, near the timber line, west base of Lassen Peak. Small phenocrysts of plagioclase and hornblende, with a few of quartz, in a reddish-gray groundmass containing much amorphous matter. Analysis by W. F. Hillebrand, record No. 668. P. R. C. 82.

E. Secretion in D. Composed essentially of plagioclase and hornblende. Analysis by Hillebrand, No. 669. P. R. C. 82. Rocks A, C, D, and E described by Diller in Bull. 150, p. 217.