IGNEOUS AND CRYSTALLINE ROCKS. 123 
99. 91 
2. MOUNT TAYLOR REGION, 
Rocks received from J. S. Diller. Analyses by T. M. Chatard, record Nos. 219, 227, 
228, 235, 271, 268, and 269. Petrographic details furnished by Diller. 
A. Lava, canyon on east side of San Mateo Mountain. Kallerudose. 
B. Andesite, canyon on east side of San Mateo Mountian. Nordmarkose. Contains 
feldspar and corroded augite, with sometimes olivine, in a groundmass of feldspar 
and a green ferromagnesian silicate. P. R. C. 1402. 
C. Quartz latite, canyon on east side of San Mateo Mountain. Lassenose. Shows 
prominent plagioclase, with augite and biotite. P.R.C. 1403. 
D. Dacite, 6 miles northeast of Grant’s. Principally plagioclase and biotite, with 
less epidote, quartz, sphene, and carbonates. P. R. C. 1401. 
E. Basait, 6 miles northeast of Grant’s. Auvergnose. Contains chiefly plagioclase, 
augite, and olivine, with much magnetite. P. R. C. 1400. 
F. Augite from E. 
G. Feldspar from E. Analysis on three-fourths gram of material. 
99.85 | 100.65 
3. COLFAX COUNTY. 
Descriptions supplied by Whitman Cross. Analyses by W. F. Hillebrand, record 
No. 1719. 
A. Phonolite, Pleasant Valley. Miaskose. Contains much nephelite, some egirite, 
alkali feldspar, a scanty dust of magnetite, and a few decomposed grains of noselite 
or-sodalite. Sp. gr., 2.619, 22°; 40.8 per cent soluble in dilute (1:40) nitric acid, of 
which soluble portion 43.5 per cent is silica. P. R.C. 1334. 
