CLARKE.] 
IGNEOUS AND CRYSTALLINE ROCKS. 
169 
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. Riesenose. 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. Alaskose. Record No. 1033. P. R. C. 531. 
S. Pitchstone, Fleetwood tunnel, Silver Cliff. Liparose. 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. 
U. Decomposition product of pitchstone, Silver Cliff. Analysis by 
W. F. Hillebrand. 
P. 
Q. 
R. 
s. 
T. 
u. 
Si0 2 
71.02 
14.27 
1.22 
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 
84.77 
AL0 3 
8.46 
Fe 2 3 
.52 
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 
.92 
CaO 
1.18 
Na 2 
K 2 
H 2 
4.11 
P 2 0, 
MnO 
.14 
.16 
.17 
BaO 
S0 3 .. 
100. 26 
100.19 
99.99 
99.99 
100. 16 
99.96 
