108 ANALYSES OF ROCKS AND MINERALS, 1880-1908. 
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4. BUFFALO PEAKS. 
Hypersthene andesite, described by Cross in Bull. 1. Contains hypersthene, 
augite, plagioclase, magnetite, and apatite. Sp. gr., 2.742, 16° Analyses made by 
W. F. Hillebrand in the Denver laboratory. 
A. Hypersthene andesite. <Andose. P. R. C. 86 and 588. 
B, C, D. Hypersthene separated from the rock. Sp. gr., of D, 3.307, 23°. In B 
and C alkalies were not tested for. In C and D all the iron is given as FeO. 
99.91 | 100.04 | 100.10 99. 59 
5. LEADVILLE REGION. 
Rocks described by Cross in Mon. XII, Appendix A. Analyses made in the Denver 
laboratory. 
A. Porphyry, Mount Zion. Toscanose. Contains orthoclase, plagioclase, quartz, 
biotite, apatite, magnetite, and zircon. Analysis by L.G. Eakins. P.R. C. 504. 
B. White or Leadville porphyry. Riesenose. Contains orthoclase, plagioclase, 
quartz, muscovite, magnetite, apatite, and zircon, with crystals which appear to be 
rutileand anatase. Sp. gr., 2.680,16°. Analysisby W. F. Hillebrand. P.R. C.587. 
C. Porphyry, summit of Mount Lincoln. Lassenose. Contains quartz, orthoclase, 
plagioclase, biotite, apatite, sphene, magnetite, zircon, and allanite. The sample. 
analyzed showed some muscovite, chlorite, and calcite. Sp. gr., 2.670, 16°. Analysis 
by W. F. Hillebrand. P.R. C. 505. 
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D. Gray porphyry, Johnson Gulch, near Leadville. Yellowstonose. Slightly 
altered. Contains orthoclase, plagioclase, biotite, and quartz, with decomposition 
products probably derived from original hornblende. Sp. gr., 2.736, 16°. Analysis 
by Hillebrand. 
