160 
ANALYSES OF ROCKS, U. S. GEOLOGICAL SURVEY. [no. 228. 
The following rocks from the Denver Basin were analyzed by L. G. 
Eakins in the Denver laboratory, but the analyses do not appear in 
the monograph. The subjoined data have been supplied by Whitman 
Cross. 
A. Enstatite-diabase-porphyry, Mount Morrison. Bandose. Con- 
tains labradorite and enstatite in a groundmass of considerable amount, 
which is colorless and cryptocrystalline, probably feldspathic, and 
carries magnetite and other indistinct ferritic matter. P. R. C. 533. 
B. Augite-andesite, Table Mountain. /. 5. 3. 3. Contains plagio- 
clase (andesine), with rare augite and biotite, in a groundmass of 
plagioclase, augite, magnetite, and minor accessories. This rock 
contained ptilolite in its vesicular equivalent. Described in Proc. 
Colorado Sci. Soc, 1886, p. 72. 
C. Augite-andesite, a pebble from the Denver beds, Table Mountain. 
Yellowstonose. A few augite and andesite phenocrysts in a groundmass 
of oligoclase, orthoclase, and quartz (?) grains, with some augite and 
magnetite. 
Si0 2 . . 
ALA- 
Fe 2 3 . 
FeO.. 
MgO. 
CaO.. 
Na 2 0. 
K 2 0.. 
H 2 0.. 
PA-- 
MnO. 
Sp. gr 
56.74 
18.80 
.15 
6.91 
5.57 
7.34 
2. 32 
.77 
1.09 
.20 
.07 
99.96 
2. 876, 27° 
59.26 
23. 63 
.30 
.57 
.31 
5.93 
4.94 
4.78 
.74 
100. 46 
2.625,31° 
59. 29 
21.27 
3. 33 
1.04 
1.12 
5.25 
3.39 
3.00 
1.63 
.23 
.21 
99.76 
2.596,14.5° 
2. PIKES PEAK DISTRICT. 
FIRST GROUP. — GRANITE. 
Described by E. B. Mathews. For description of A, C, E, and F 
see Journ. Geol., vol. 8, p. 214. Analyses by W. F. Hillebrand, 
record No. 1470. 
A. Granitite, Sentinel Point, western part of Pikes Peak massif 
Alaslcose. Contains microcline, microcline-perthite, quartz, biotite, a 
little oligoclase, and accessory fluorite, apatite, zircon, sphene, mag- 
netite, and allanite. P. R. C. 67 and 600. 
B. Granitite, near road between Florissant and the Platte River. 
