G. Wall rock, Federal Loan mine. A siliceous argillite, of sedimentary origin. Contains quartz, feldspar, biotite, pyrrhotite, and a little calcite. Analysis by Hillebrand, No. 1478.

H. Altered wall rock, Providence mine. Derived from granodiorite. Analysis by Hillebrand, No. 1478.

I. Altered wall rock, Providence mine, back vein. Derived from granodiorite and schist. Analysis by Hillebrand, No. 1478.

J. Altered wall rock, North Star mine. Derived from uralite-diabase. Contains quartz, sericite, calcite, pyrite, and sphene. Analysis by Hillebrand, No. 1478.

K. Altered country rock, Idaho mine. Derived from serpentine. Analysis by Hillebrand, No. 1478.

L. Bleached country rock, next to vein, Osborne Hill mine. Derived from sandstone. Analysis by George Steiger, record No. 1541. M. Altered wall rock, Empire mine. Derived from granodiorite. Analysis by Steiger, No. 1541. Sp. gr., 2.782, 20°.

N. Altered wall rock, Ebaugh tunnel. Derived from granodiorite. Mainly quartz and sericite, with pyrite, apatite, sphene, and carbonates. Analysis by Steiger, No. 1541. Sp. gr., 2.747, 20°.

O. Altered wall rock, Federal Loan mine. argillite. Analysis by Steiger, No. 1541.

Derived from siliceous

7. PLACER COUNTY.

First, a series of rocks from the Ophir mining district, described by Lindgren in 14th Ann., p. 249. Analyses by W. F. Hillebrand, record Nos. 1419, 1433, 1434.

A. Granodiorite, quarries at Lincoln, 8 miles west of Ophir. Contains feldspars, quartz, biotite, and hornblende.

B. Pyritiferous amphibolite, Conrad tunnel. Partly altered. Contains pyrite, hornblende, magnetite, feldspars, quartz, epidote, chlorite, a few scales of mica, rutile, and carbonates. Sp. gr. 2.901, 23°.

C. Dike rock, near camptonite, Casey's tunnel, Flat Ledge, Duncan Hill. Contains hornblende, feldspars, pyrite, and apatite, with secondary epidote and quartz.

D. Altered wall rock, Mina Rica vein. Sp. gr. 2.979, 20°.

E. Altered wall rock, Plantz vein. These rocks, D and E, contain quartz, muscovite, a little chlorite, pyrite, and sphene, with carbonates of calcium, magnesium, and iron.

Second, rocks from other localities in Placer County. Studied also by Lindgren, who furnishes the petrographic data. Analysis A by W. H. Melville, record No. 1346; B, C, D, and E by W. F. Hillebrand, record No. 1419.

A. Granite, Rocklin. A normal granite, containing quartz, orthoclase, plagioclase, biotite, muscovite, magnetite, apatite, and zircon, with some secondary chlorite and epidote derived from the biotite. Described by Lindgren in Bull. 150, p. 170. P. R. C. 66.

B. Granodiorite, Donner Pass. Contains plagioclase, orthoclase, quartz, hornblende, biotite, and sphene.

C. Gabbro, 2 miles south of Emigrant Gap, on road to Onion Valley. Contains biotite, hypersthene, diallage, plagioclase, and orthoclase.

D. Gabbro, same locality as C. Contains hypersthene, diallage, plagioclase, and orthoclase.

E. Augite-granite, southeast spur of English Mountain. Contains "basic" plagioclase, augite, and quartz.

8. ELDORADO COUNTY.

A. Granitite, Placerville canal, one-third mile north of Ditch Camp No. 7. Collected by W. Lindgren, who reports it as containing biotite, orthoclase, plagioclase, and quartz. Analysis by George Steiger, record No. 1591.

B. Granodiorite, 2 miles south of Silver Lake Hotel. Collected by Lindgren, who reports it as containing hornblende, biotite, plagioclase, and quartz. Analysis by Steiger, No. 1591. Analyses A and B are published by Lindgren in Amer. Journ. Sci., 4th ser., vol. 3, p. 306.

C. Porphyrite, 1 mile southwest of Latrobe. Published by Turner in 17th Ann., Part I, p. 521. Contains abundant plagioclase, less augite, calcite or dolomite, iron disulphide, a little chlorite, and secondary greenish mica. Analysis by W. F. Hillebrand, record No. 1432. P. R. C. 721.