82 
ANALYSES OF ROCKS, U. S. GEOLOGICAL SURVEY. 
[NO. 228. 
3. MENOMINEE RIVER. 
1. STURGEON FALLS GABBRO. 
From Sturgeon Falls, Menominee River, sec. 27, T. 39 N., R. 29 W., 
Michigan. Described by Williams, Bull. 62, p. 67. 
A. Saussurite-gabbro. Auvergnose. Contains plagioclase, almost 
wholly altered to saussurite, diallage, hornblende, and ilmenite, with 
quartz, calcite, and chlorite as alteration products. 
B. The same, altered and somewhat schistose. Feldspar much 
altered into calcite, with secondary quartz and sericite; pyroxene and 
hornblende changed to chlorite. Leucoxene common. 
C. Light-gray, silvery schist, derived from gabbro. Contains chlo- 
rite, calcite, and a little quartz, with remnants of feldspar and some 
leucoxene. Analyses by R. B. Riggs, record Nos. 389, 390, 391. 
Material dried at 105°. Ti(X undetermined. 
Si0 2 . 
A1 2 3 
Fe 2 :! 
FeO. 
MgO 
CaO. 
Na 2 
K 2 0. 
H 2 0. 
CO,. 
A. 
51. 46 
14.35 
3.90 
5.28 
9.54 
9.08 
2.92 
.24 
3.30 
.20 
B. 
38. 05 
24.73 
5.65 
6.08 
11.58 
1.25 
2.54 
1.94 
7.53 
.93 
100. 27 
45.70 
16.53 
4.63 
3.89 
9.57 
4.28 
.55 
3.82 
4.70 
5.95 
99.62 
