58 
ANALYSES OF ROCKS, U. S. GEOLOGICAL SURVEY. [no. 228. 
To these may be added three analyses of feldspars from the pegma- 
tite of Jones Falls, Baltimore. Described by S. L. Powell, in Johns 
Hopkins Univ. Circular, vol. 12, p. 49. Analyses by W. F. Hillebrand, 
record No. 1421. 
O. Flesh-colored microcline. 
P. Green microcline. 
Q. Albite-oligoclase, near Ab 4 An. 
Si0 2 
A1A 
Fe 2 3 --- 
FeO 
MgO 
CaO 
Na 2 
K 2 
H 2 0at 100°.... 
H 2 above 100° 
SrO 
BaO 
o. 
65.06 
18.41 
trace 
.04 
.26 
1.60 
14. 30 
.04 
.26 
trace 
.13 
100. 10 
68.48 
16.11 
.20 
.17 
.03 
.23 
1.27 
12.99 
.06 
.26 
trace 
.05 
99.85 
63.72 
22.26 
trace 
.06 
3.58 
8.98 
.76 
.09 
.43 
trace 
99.88 
P contained a little unseparated quartz. All three contained traces of lithia. In 
O and Q the traces of iron were weighed with the alumina. 
