150 
ANALYSES OF ROOKS, U. S. OEOLOGICAL SURVEY. 
[BUM,. 168. 
P. Rhyolitic tuff, a lake-bed deposit east of the Blue Mountains. 
Mainly composed of glassy rhyolite dust. 
Q. Devitrified pitchstone, the gangue of ptilolite, 3 miles southeast 
of Silver Cliff. Shows feldspar, quartz, and barite. Described by 
Cross and Eakins in Amer. Journ.* Sci., 3d series, vol. 44, p. 96. Record 
No. 1342. P. R. C. 590. 
R Pitchstone, Rosita. Record No. 1033. P. R. C. 531. 
S. Pitchstone, Fleetwood tunnel, Silver Cliff. P. R. C. 523. 
T. Alteration product of S. Consists mainly of silica and kaolin. 
Record No. of S and T, 1034. P. R. C. 591. 
p. 
71.02 
14.27 
1.22 
Q. 
R. 
s. 
T. 
Si0 2 .-. 
65.67 
13.48 
1.51 
73.11 
13.16 
.62 
.23 
.19 
.54 
2.85 
5.10 
4.05 
71.56 
13.10 
.66 
.28 
.14 
.74 
3.77 
4.06 
5.52 
71.71 
12.36 
1.10 
AL0 3 
Fe,(X 
FeO 
MgO 
trace 
1.38 
2.28 
3.97 
6.12 
.31 
2.41 
1.52 
2.42 
12.27 
trace 
trace 
.32 
.28 
1.21 
1.11 
.17 
.36 
11.. 97 
CaO 
Na 2 
K 2 
H 2 
P„0« 
MnO 
.14 
.16 
.17 
BaO 
so 3 
100. 26 
100. 19 
99.99 
99.99 
100.16 
