IGNEOUS AND CRYSTALLINE ROCKS. 71 
J. Sanidine quartz rhyolite, Sheridan volcano. Analysis by G. Steiger, record 
No. 2154. 
K. Rhyolite, Madison Plateau. Like I. Near alaskose. Analysis by Whitfield, 
No, 427. 
L. Trachytic rhyolite, Elk Creek. Lassenose. Analysis by Whitfield, No. 428. 
Reported by Iddings as containing sanidine, labradorite, and little biotite, in a 
groundmass of quartz and alkali feldspar. 
G H I Ti k L 
SOU G csod cma ee eeerplale eraerar si piacie ine memeber wlenan ae hentne 75.71 | 75.34 | 75.89) 77.65 | 75.19 64.65 
PALO i832 25 suacsarots es amnatnard attcasrniaeAme on cienondeae Aes wean J1.11 ) 12.51 12.27} 11.50} 13.77 17.80 
Me a0 oe ma sncreas daisanacicnns dban een askan da tee oemne ues 1 42 4.12: 1.21 61 2.33 
DED wis aracayatre a ula dee teeta eeed A adiaas S&icm mies unene ee 37 1.55 1.37 26 1.37 2.10 
MEO a crrcrsctemrnepodels sepreceds besa vices aesiath sc histaiegecansinin aentoee 08 32 .29| none 09 81 
CaO 88 1.07 86 59 68 1.73 
KO... 
HO at 105°... 
M. Trachytic rhyolite tuff, Two Ocean Pass. Analysis by Whitfield, No. 906. 
Reported by Iddings as containing sanidine, labradorite, biotite, magnetite, and 
augite, in a somewhat altered, glassy groundmass. Also contains fragments of andesite. 
N. Glassy trachyte, approaching rhyolite, Sunset Peak, Bear Gulch. Toscanose. 
Contains phenocrysts of sanidine, plagioclase, and biotite. See Iddings, Bull. Philos. 
Soc. Washington, vol. 12, p. 205; also Mon. XXXII, pt.2. Analysis by L. G. Eakins, 
record No. 1378. 
O. Altered rhyolite, ‘‘Iron Pot,’’ Lower Basin. Collected by W.H. Weed. Analy- 
sis by Whitfield, No. 546. 
P. Dacite porphyry, Echo Peak. Near alaskose. 
Q. SameasO, Mount Holmes. <Alsbachose. Analyses O and P by Whitfield, Nos. 
421, 422. Reported by Iddings as containing plagioclase, probably oligoclase, quartz, 
little biotite, and magnetite. 
R. Mica dacite porphyry, Bunsen Peak. Lassenose. Analysis by Whitfield, No. 
419. Reported by Iddings as containing oligoclase-andesine, quartz, biotite, little 
magnetite, apatite, and zircon. 
