Gabbroid Rocks of Minnesota. — Wincliell. 163 
the writer for study by the director of the Geological and Na- 
tural History Survey of Minnesota : 
1. Olivine gabbro (1136), collected by M. E. Wadsworth, from a 
point one-half a mile west of the line between sec. 31, 62-11, and sec. 
6, 61-11, in T. 61. near Birch lake. Shows a slight tendency toward 
the ophitic texture. 
2. Diabase poor in olivine (954). collected by N. H. Winchell from 
the east side of Birch lake on N. W. K sec. 17, 61-11. Called "gab- 
bro" by N. H. Winchell, on account of a distinct tendency toward the 
granular texture. 
3. Olivine diabase (1843), collected by N. H. Winchell from the 
extremity of Pigeon point. Sometimes called "gabbro"* to distin- 
guish it from the fine-grained diabases which abound in the same lo- 
cality. 
4. Plagioclasyte (336E), collected by A. H. Elftman from the 
summit of Carlton peak. 
5. Troctolyte (514). collected by N. H. Winchell from near Du- 
luth. Also called forellenstein. 
6. Silicoferrolyte (960), collected by N. H. Winchell from a low 
ridge of fifteen rods from the shore of Birch lake, S. W. 54, sec. 24, 
64 — 12. Called "olivinitic iron ore," in the reports of the Geological 
and Natural History Survey of Minnesota. 
7. Quartz gabbro (8S4G and 854 (A) G), collected by U. S. 
Grant, from S. E. Va, S. W. ^ sec. 12, 64—6, southwest shore of small 
lake near Little Saganaga lake. 854 (A) G is the porphyritic variety. 
8. Orthoclase gabbro (i797). collected by N. H. Winchell, from 
Duluth. 
9. Hornblende gabbro (i797), collected by N. H. Winchell, from 
Duluth. 
10. Cordierite noryte (983), collected by N. H. Winchell, from sec. 
15, 63 — 9, not far from Snowbank lake. One of the "muscovadytes" 
of the Minnesota Survey. 
It is the purpose of the present article to study these types 
from the petrographic, mineralogical, and chemical points of 
view. Their geological relationships, their taxonomic position 
and all questions of general geology will form no part of the 
study. In a general way these questions will be considered as 
settled according to the principles and conclusions of the final 
report of the Minnesota Survey. The field relations and gen- 
eral geological relations will be given for each type, so far as 
they have been established by other studies, in order that they 
*See Bayley: The eruptive and sedimentary rocks of Pigeon point, 
Minnesota: Bull. 109. U. S. Geol. Survey, 1893, et al. 
