96 
ANALYSES OF ROOKS, U. S. GEOLOGICAL SURVEY. 
[no. 228. 
F. Average gabbro, S. quarter post, sec. 35, T. 61 N., R. 12 W. 
Hessose. Described by Bayley in Journal of Geology, vol. 1, p. 688. 
Contains plagioclase, olivine, pyroxene, and magnetite. Analysis by 
H. N. Stokes, record No. 1267. 
G. Feldspar, from preceding gabbro. Analysis by W. F. Hille- 
brand, record No. 1308. 
H. Feldspar, from gabbro east side of North Fowl Lake. Analysis 
by Hillebrand, No. 1308. 
* I. Feldspar, from gabbro, NW. £of SE. ±of sec. 23, T. 62 N., R. 10 W. 
J. Feldspar, from gabbro, center of sec. 25, T. 61 N., R. 8 W. 
K. Feldspar, from gabbro, Duluth and Iron Range Railroad. 
Analyses 1, J, and K by Hillebrand, record No. 1115. 
H, I, J, and K analyzed for W. S. Bayley, but analyses hitherto 
unpublished. 
Si0 2 s 
A1 2 3 
Fe 2 3 
FeO 
MgO 
CaO 
Na 2 
K 2 
H 2 Oatl00°.... 
H 2 above 100° 
Ti0 2 
P 2 5 
NiO 
MnO 
SrO 
46.45 
21.30 
.81 
9.57 
7.90 
9.83 
2.14 
.34 
.14 
1.02 
1.19 
.02 
.04 
trace 
100. 75 
51.89 
29.68 
.32 
.37 
.38 
12.62 
3.87 
.50 
.07 
.39 
H. 
62.71 
19.20 
1.08 
.93 
.81 
.44 
2.96 
10.41 
.23 
.92 
trace 
trace 
trace 
100.09 99.69 
52.50 
30. 15 
.47 
.15 
.10 
12.82 
3.72 
.53 
.25 
trace 
100.69 
52. 61 
29.80 
.57 
.23 
.20 
12.25 
3.80 
.53 
.29 
trace 
trace 
100.28 
K. 
53.45 
29.77 
.33 
.15 
.11 
11.33 
4.33 
> ■ 
23 
trace 
100. 38 
