IGNEOUS AND CRYSTALLINE ROCKS. 149 
6. NEVADA CITY AND GRASS VALLEY. 
Rocks of a mining district in Nevada County, described by Lindgren in 17th Ann., 
pt. 2, p. 1. 2 
A. Granodiorite, 1 mile southeast of Nevada City. Yellowstonose. Contains horn- 
blende, biotite, quartz, plagioclase, orthoclase, magnetite, apatite, sphene, and pyrite. 
Analysis by W. F. Hillebrand, record No. 1478. P. R. ©. 1521. 
B. Granodiorite, Kate Hayes Hill, Grass Valley. Harzose. Contains plagioclase, 
orthoclase, quartz, hornblende, pyrite, magnetite, apatite, sphene, and zircon. 
Analysis by Hillebrand, No. 1478. 
C. Hornblende porphyrite, Nevada City. Tonalose. Contains feldspar, horn- 
blende, quartz, epidote, sericite, and biotite. Analysis by H. N. Stokes, record No. 
1531. 
D. Quartz porphyrite, New Ophir claim, Grass Valley. Tonalose. Contains 
plagioclase, quartz, uralite, epidote, and augite, and hornblende altered into chlorite. 
Analysis by Stokes, No. 1531. 
E. Diabase, near Maryland mine, Grass Valley. Ornose. Contains feldspar, augite, 
hornblende, ilmenite, pyrrhotite, pyrite, and some chlorite. Analysis by Stokes, 
No. 1522. 
F. Diabase, Grass Valley. Bandose. Contains feldspar, pyroxene, hornblende, 
ilmenite, pyrrhotite, pyrite, and chlorite, and probably a little quartz. Analysis by 
Stokes, No. 1522. 
Kg Ne ata me 
20 at 110°.... 
H20 above 110° 
G. Wall rock, Federal Loan mine. A siliceous argillite, of sedimentary origin. 
Contains quartz, feldspar, biotite, pyrrhotite, and a little calcite. Analysis by Hille- 
brand, 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. 
15619—Bull, 419—10-——11 
