52 
ANALYSES OF ROCKS, U. S. GEOLOGICAL SURVEY. [no. 228. 
2. (1ABBKO AND DIORITE. 
Rocks A to E, inclusive, described by G. IL Williams, but not in 
detail, in 15th Ann., pp. 673, 674. Some of the rocks, with other 
analyses, arc discussed by him in Bull. 28. Analyses by W. F. Hille- 
brand, record No. 1422. 
A. Olivine-gabbro, Orange Grove, Baltimore County. IV. T. i 2 . & 
Contains plagioclase, diallage, hypersthene, fresh olivine, magnetite, 
and apatite, and sometimes hornblende, 
B. Hypersthene-gabbro, Wetheredville, Baltimore County. Keda- 
lekose. Rich in hypersthene and diallage, with plagioclase, magnetite, 
and apatite. 
C. Gabbro-diorite, Ilchester, Howard Caunty. Hesnose. A coarse 
anorthite-hornblende rock, probably an altered gabbro. 
D. Biotite-diorite, Triadelphia, Montgomery County. Bandose. 
E. Biotite-diorite, Georgetown, D. C. Bandose. 
To these may be added an apparently unpublished analysis made for 
Williams by L. G. Eakins, record No. 1350, as follows: 
F. Hornblende-diorite, Rock Creek tunnel shaft. Washington, D. C. 
///. .',. ',. J h 5. Relations to E not stated. 
A. 
48.91 
s. si 
1.04 
9. 52 
15. 19 
L4.69 
.64 
.10 
.07 
.52 
.37 
trace 
B. 
14. 76 
L8.82 
2. L9 
4.73 
LI. 32 
14.58 
.89 
.11 
.17 
2.36 
.13 
none 
C. 
D. 
E. 
F. 
SiO 
4:;. -ri 
22. 37 
.81 
9.25 
5. 75 
L3.34 
1.24 
1.13 
.09 
1.54 
1.25 
.10 
55. 97 
15.60 
1.21 
6.28 
6.83 
7.31 
2. 23 
1.25 
.18 
1.85 
1.11 
.16 
5(5.41 
15. 19 
1.60 
6.24 
7.18 
6.77 
2.21 
1.34 
.08 
2.00 
.69 
.05 
.14 
.05 
.11 
trace 
56. 18 
AL( ), 
14.76 
Fe.,0* 
2.12 
FeO 
6.98 
MO 
8.11 
CaO 
7.97 
Na 2 
1.62 
K 2 
.80 
H,Oatl00° 
J 1.37 
H 2 above 100° 
Ti0 2 
P o 0r 
.08 
SnO ZrO ? 
Cr 2 0, - --- 
.15 
.16 
trace 
.08 
.15 
trace 
trace 
.06 
trace 
.04 
.08 
trace 
MnO 
.17 
Li 2 
100. 17 
100. 29 
100. 35 
100. 10 
100. 06 
100. 16 
