112 ANALYSES OF ROCKS AND MINERALS, 1880-1908. 
9, LA PLATA MOUNTAINS. 
Rocks described by Whitman Cross in Folio 60. 
A. Monzonitic facies of diorite mass. Akerose. Contains augite, hornblende, 
plagioclase, and orthoclase in large amount, with biotite, quartz, sphene, apatite, and 
magnetite as subordinate constituents. Also secondary chlorite, muscovite, and 
calcite. Analysis by W. F. Hillebrand, record No. 1640. Sp. gr., 2.79, 21°. De- 
scribed by Cross in 21st Ann., pt. 2. P. R. ©. 1284. 
B. Diorite porphyry, Deadwood Gulch. Akerose. Contains phenocrysts of horn- 
blende, plagioclase, occasional quartz, sphene, apatite, and magnetite in a groundmass 
of orthoclase, plagioclase, and quartz. Also secondary epidote, chlorite, and calcite. 
Analysis by Hillebrand, record No. 1636. Sp. gr., 2.677, 24°. A trace of sulphur is 
present. Described by Cross in 21st Ann., pt. 2. P. R. 0. 1283." 
C. Augite syenite, between Tirbircio and Schurman gulches. Monzonose. Con- 
tains much alkali feldspar, some oligoclase, augite, biotite, and hornblende, with a 
little titanite, magnetite, and apatite. Analysis by H. N. Stokes, record No. 1764. 
Sp. er., 2.704, 25° ~P. R. C. 1286. 
D. Augitic monzonite, Babcock Peak. Andose, Contains orthoclase and plagio- 
clase in about equal amounts, with augite and hornblende, and a little quartz, titanite, 
magnetite, and apatite. Analysis by Stokes, record No. 1764. Sp. gr., 2.767, 26°. 
Described by Cross in 21st Ann., pt. 2. P. R. C. 1285. 
E. Porphyritic lamprophyre, allied to camptonite, Snowstorm Peak. Kental- 
lenose. Contains numerous phenocrysts of green hornblende, augite, and plagioclase, 
in a groundmass of plagioclase, orthoclase, augite, magnetite, and apatite. Some 
secondary calcite. Analysis by Hillebrand, record No. 1640. Sp. gr., 2.906, 21°. 
P. R. C. 1287. 
f. Basic dike rock, Indian Trail Ridge, La Plata quadrangle. Camptonose. 
Contains phenocrysts of green hornblende and colorless diopside in a subordinate 
groundmass of plagioclase, orthoclase (?), augite, magnetite, and apatite. Much 
secondary calcite and some serpentine. Analysis by W. F. Hillebrand, record No. 
1640. Sp. gr., 2.912, 19.5°. P. R. C. 1288. 
A B Cc. D. E F 
SO ge aaieae acarerereetaninariies eriaciies onsets aieimmeeeieter 55.53 | 60.44] 59.79 | 57.42) 47.25 43. 98 
AN Og e.c. ac retnecerrenaiishia coe heen alee aa eee ocean 16.78 | 16.65] 17.25} 18.48] 15.14 13. 30 
PCO gessiscizdiardarrqumiavewen simcinercemn cinch cineae ccleeareds 4.06 2.31 3. 60 3.74 5.05 3. 67 
FeO. 3. 35 3.09 1.59 2.10 4.95 6. 92 
MgO 3.00 2.18 1,24 171 6. 87 7.03 
CaO. 6.96 4,22 3.77 6.84 9. 98 10. 66 
Naz2O 4.31 5.18 5.04 4.52 39 2.15 
FO at MNO 1a cicinig eiciatisiacmaomauencioodcnemnaseewenee - 09 36 a9 - 08 
‘ . . 4 2: 
RO, oecsscisiass -| 3.57 2.71 5.05 3.71 2. 60 1.64 
- 40 
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