A. Winchell on the Animike in Minnesota. 15 
purpose of this paper to contribute a few facts suited to throw 
light on the question. 
The Animike formation covers an extensive area stretching 
from Thunder bay of the north shore of lake Superior, south- 
westward as far as Duluth, and still beyond to the Mississippi 
river. The lake-shore belt, however, from Grand Portage, for 
an average width of about twenty miles, is occupied by rocks of 
the Kewenian series. The Animike rocks for the greater part, 
are evenly and thinly laminated, and have a southerly dip along 
the international boundary of about five to ten degrees. They 
embrace a great thickness of black carbonaceous argillytes, 
varying to pure slaty argillytes, black magnetitic slates, often 
rich in iron, and siliceous schists sometimes quite purely siliceous 
and I'anging in color to chalcedonic, flinty, cherty and red- 
jaspery. The magnetitic horizon presents, over an extensive 
area west of Gunflint lake, on the boundary, remarkable de- 
posits of valuable ore ranging from lean to nearly j^ure magne- 
tite. At a lower horizon are beds of ferruginous (perhaps 
sideritic) dolomite, and compact sandstone holding a considera- 
ble percentage of fine granular orthoclase. The territory of 
the formation is characterized by high precipitous bluffs facing 
northward, but sometimes westward, and generally capped by a 
thick table of gabbro, which, on the eroded side, presents rude 
columnar aspects.' 
Sir William Logan regarded the formation as the "Lower 
Group" of the copper-bearing series. Mr. Bell in his reports 
of 1866-9 and 1873-3, expresses the same view. Macfarlane,^ 
on the contrary, described it as newer than the copper-bearing 
series. Dr. T. S. Hunt, also, who was the first to propose the 
name "Animike," (from the Chippewa for "thunder")^ at first 
considered the formation as lying above the copper-bearing 
1 Full descriptions of the formation may be found in Logan's Geology 
of Canada, 1863, pp. 66-70, and more extended, in Irving's Copper-bearing 
Rocks of lake Superior. Monographs of the United States geological 
survey, vol. v, pp. 367-386; also Third annual report of U. S. Geol. Sur- 
vey, pp. 157-163. The reader may consult also, Bell, in Geol. Surv. of 
Canada, Report for 1866-1869, pp. 318-19, and Rep. 1872-3, pp. 92-3. 
2 Canadian Naturalist, New Series, iii, 252; iv, 38. 
3 Hunt, Trans. Am. Inst. Mining Engineers, vol. i, p. 339. 
