44 ANALYSES OF ROCKS, U. S. GEOLOGICAL SURVEY. [bull. 168. 
2. GABBRO AND DIORITE. 
Rocks A to E, inclusive, described by G. H. Williams, but not in 
detail, in 15th Ann., pp. 673, 674. Some of the rocks, with other 
analyses, are discussed by him in Bull. 28. Analyses by W. F. Hille- 
brand, record No. 1422. 
A. Olivine-gabbro, Orange Grove, Baltimore County. Contains 
plagioclase, diallage, hypersthene, fresh olivine, magnetite, and apa- 
tite, and sometimes hoynblende. 
B. Hypersthene-gabbro, Wetheredville, Baltimore County. Rich 
in hypersthene and diallage, with plagioclase, magnetite, and apatite. 
C. Gabbro-diorite, Ilchester, Howard County. A coarse anorthite- 
hornblende rock, probably an altered gabbro. 
. D. Biotite-diorite, Triadelphia, Montgomery County. 
E. Biotite-diorite, Georgetown, D. C. 
To these may be added an apparently unpublished analysis made for 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. 
Relations to E not stated. 
A. 
B. 
c. 
D. 
E. 
F. 
Si0 2 
48.91 
8.81 
1.04 
9.52 
15.19 
14.69 
.64 
.10 
.07 
.52 
.37 
trace 
44.76 
18.82 
2.19 
4.73 
11. 32 
14.58 
.89 
.11 
.17 
2.36 
.13 
none 
43.42 
22.37 
.81 
9.25 
5.75 
13. 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 
56.41 
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 
14.76 
2.12 
6.98 
8.11 
7.97 
1.62 
.80 
} - 
A1 2 3 
Fe 2 3 
FeO 
MgO 
CaO 
Na 2 
K 2 
H 2 Oatl00°... 
H 2 above 100° 
Ti0 2 
P,0, 
.08 
Sn0 2 , Zr0 2 ?... 
Cr 2 3 
.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 
