12 ANALYSES OF ROCKS AND MINERALS, 1880-1908. 
S. Mica dacite porphyry, Birch Hills. Lassenose. Like Qin composition. Analy 
sis by Whitfield, No. 718. 
T. Hornblende-mica andesite porphyry, Fan Creek. Yellowstonose. Analysis b: 
Whitfield, No. 713. Reported by Iddings as containing andesine-oligoclase, horn 
blende, and biotite in a groundmass of feldspar (probably oligoclase and orthoclase) 
with a little magnetite, biotite, and hornblende. 
U. Hornblende-mica andesite porphyry, Gray Peak. Lassenose. Analysis by Whit 
field, No. 715. Composition similar to that of 8. ; 
R Ss Tt U. 
65. 63 65.6 
17.00 17.2 
2.55 3.0 
1.19 1.2 
2.03 1.7 
3.48 1.9 
4,42 6.7 
1.64 2.4 
2.00 1.0 
trace non 
07 «2 
none trac 
04 
trace trac 
trace trac 
+27 1 
100.32 | 100.7 
V. Hornblende-mica andesite, Crescent Hill. Yellowstonose. Analysis by Whit 
field, No. 432 Reported by Iddings as containing oligoclase-andesine, biotite, anc 
subordinate decomposed hornblende, in a groundmass of feldspar and quartz, with : 
little magnetite and biotite. 
W. Hornblende andesite, Tower Creek. Dacose. Analysis by Gooch, No. 117 
Reported by Iddings as containing plagioclase, hornblende, and a little augite. 
X. Pyroxene andesite, Agate Creek. Tonalose. Analysis by Whitfield, No. 432 
Reported by Iddings as containing augite, hypersthene, labradorite, and magnetite 
in a glassy microlitic groundmass. 
Y. Rhyolitic perlite. Toscanose. Described by Iddings, Bull. 150, p. 153. Anal 
ysis by H. N. Stokes, No. 1314. From a bluff opposite the Midway Geyser Basin 
Reported by Iddings as containing quartz, sanidine, plagioclase, and rarely augit 
and magnetite, with microscopic zircon and apatite, in a glassy groundmass. P. R 
C. 61. 
Vv, Ww. x. Y. 
61.56 | 61.45 73.8 
14.73 | 15.07 12.4 
4.47 4. 46 3 
1.23 1.18 9 
3. 57 3. 02 22 
4, 87 5. 37 1.0 
5.10 4.00 2.8 
2.24 1.22 5.3 
1,42 1. 23 2.7 
87 2.80 |.....-. 
