166 
ANALYSES OF ROCKS, U. S. GEOLOGICAL SURVEY. 
[no. 228. 
3. SILVER CLIFF AND ROSITA. 
Rocks described by Cross, mostly in 17th Ann., Part II, p. 263. 
Also, partly in Proc. Colorado Scientific Soc, vol. 2, p. 228. Analy- 
ses, with one exception, by L. G. Eakins. Those with record num- 
bers attached were made in the Washington laboratory; all others in 
the laboratory at Denver. 
A. Peridotite, Cottonwood Gulch. Custerose. Contains hornblende, 
biotite, hypersthene, olivine, a little plagioclase, apatite, pyrrhotite, 
and sillimanite (?). P. R. C. 519. 
B. Augite-diorite, Mount Fairview, Rosita Hills. Salemose. Con- 
tains augite, biotite, labradorite, and accessory orthoclase, olivine, 
magnetite, and apatite. Sp. gr., 2.870, 32°. Olivine a subordinate 
constituent. P. R. C. 526. 
C. The same as B, but with orthoclase in much larger amount. 
Akerose. Sp. gr., 2.768, 34°. Record No., 1091. P. R. C. 529. 
D. Trachyte, Game Ridge. Phlegrose. Contains sanidine, plagio- 
clase, a little biotite, magnetite, apatite, and zircon in agroundmass of 
orthoclase, with a little quartz. Sp. gr., 2.592, 29°. P. R. C. 70 and 
521. 
E. Trach} T te, dark-colored dike. Pulashose. Contains more mag- 
netite than D, but otherwise the two are practically identical. Sp. 
gr., 2.621, 21°. P. R. C. 589. 
Si0 2 _. 
A1A- 
Fe 2 < > 3 
FeO_. 
MgO. 
CaO.. 
Na.,0 . 
K 2 0.. 
H 2 0.. 
Ti 2 . 
P 2 5 . 
MnO. 
C0 2 .. 
CL... 
17 
40 
100. 09 
50. 47 
is. 73 
4.19 
4.92 
3.48 
8.82 
4.62 
3.56 
.58 
.51 
.10 
.11 
trace 
trace 
100. 09 
53. 80 
20. 13 
3. 57 
2. 63 
2. 26 
5. 60 
5. 20 
4.49 
.90 
.43 
.56 
.29 
99.86 
66. 03 
18.49 
2.18 
. 22 
.39 
.96 
5.22 
5. 86 
.85 
.04 
trace 
trace 
100. 24 
65. 41 
18.78 
.94 
.72 
.16 
1.58 
5.91 
5.41 
1.38 
trace 
trace 
100. 29 
