132 Hie Ainetican Geologist. September, i898 
it seems advisable to omit these at present. The same may be 
said of the Logan sills in the Animikie. In giving referenc- 
es, the numbers given in the text refer to the number of the 
article in the bibliography of the literature upon the Kewee- 
nawan area given in the March number of the Geologist. 
Chapter III. The Gabbro Member. 
Surface area. The gabbro forms the outer or northern 
member of the Keweenavvan series. The general shape of the 
area is crescentic with the concave side towards lake Superior. 
The horns of the crescent are located, the one near Duluth and 
the other near East Greenwood lake, T. 64, N., R. 2 E. The 
chord connecting them is 125 miles long and runs northeast 
and southwest. The maximum width of the area is 25 miles. 
The surface area is about 2,400 square miles in extent. 
The northern boundary of the gabbro is quite regular and 
comes into contact with all of the pre-Keweenawan forma- 
tions recognized in northeastern Minnesota. In Ts. 49 and 50 
N. R. 15 W. the gabbro is in contact with the Animikie slates 
of the Saint Louis river valley. Continuing northward the 
contact of the formations is concealed by glacial drift for the 
next sixty miles. In the vicinity of Birch lake. T. 61 N., R. 
12 W., the gabbro is found in contact with the iron-bearing 
member of the Animikie. Within the next twenty miles 
northeast from Birch lake the contact is with the White Iron 
lake granite of pre-Animikie age. Extending eastward to 
lake Gabemichigama the gabbro cuts and lies upon the 
Lower Keewatin, Upper Keewatin and the Snowbank lake 
granite. Between Gabemichigama and Gunfhnt lakes the 
gabbro is in contact with the Animikie, Keewatin and some 
ancient greenstones (gabbros, etc.), probably of Archaen age. 
From T. 65 N. R. 4 W. to the eastern extremity the gabbro is 
in contact with the iron-bearing, black slate and graywacke 
slate members of the Animikie. 
The southern boundary of the gabbro is irregular on ac- 
count of the invasions of other members of the Keweenawan 
series. From the south side of East Greenwood lake the 
boundary passes westward for thirty miles and turns south 
and east through Brule lake along the Brule river valley to 
the east side of T. 63 N., R. i W. In the vicinity of Brule 
Mt. and Eagle Mt. the limit of the gabbro zigzags and finally 
