34 
ANALYSES OF ROCKS, U. S. GEOLOGICAL SURVEY. [bull. 168. 
A. The rock. 
B. The separated feldspar. 
Si0 2 
A1 2 3 -------- 
Fe 2 3 
FeO 
MgO 
CaO 
Na 2 
K 2 w 
H 2 at 110° . . . 
H 2 at redness 
Ti0 2 ? 
P 2 5 
MnO 
100. 42 
70.23 
65.66 
15. 00 
20.05 
1.99 
trace 
undet. 
trace 
.38 
.18 
.33 
.67 
4.98 
6.56 
4.99 
6.98 
.91 
.04 
1.28 
.37 
.03 
undet. 
.06 
undet. 
.24 
.13 
100. 64 
Feldspars from schists of Berkshire County. Described by Wolff, 
Mon. XXIII, pp. 60 and 187. All albite. Analyses by R. B. Riggs, 
record Nos. 507 and 567. 
A. From feldspathic schist, central shaft of the Hoosac tunnel. P. 
R. C. 129. 
B, C. From the porphyritic mica-schist of Greylock Mountain. 
Si0 2 
Al 2 3 ,Fe 2 3 
MgO 
CaO 
Na 2 
Ignition 
MnO... 
A. 
69.69 
18.60 
.20 
trace 
10.28 
.40 
.42 
99.59 
B. 
68.08 
20.11 
(?) 
trace 
11.00 
.36 
.31 
trace 
99.86 
67.83 
19.92 
(?) 
trace 
11.65 
.25 
.12 
trace 
99.77 
FeA l ess than 0.5 in any case. 
