154 TJie Amcvican Geologist. September, 1900 
the Polar sea. It is roughly triangular in outline with its base 
toward the north. The surface of this whole country has well 
marked characteristics ; it is rarely or never mountainous, and 
at the same time it is exceptional to find in it a level plain of 
any extent ; it is generally wooded except in the far north 
where the climate is too severe. The contours are so irregular 
that it is pre-eminently a country of lakes* and hills, which 
give it a rugged charm of its own. 
Perhaps the most marked irregularity in the outline of this 
huge triangle is caused by an extension from the western side 
toward the southwest. This projection occupies the northeast- 
ern part of the state of Minnesota, and the adjacent portions 
of Canada, lying to the north and west of lake Superior. With- 
in this small area are found the watersheds separating the head 
waters of three great river systems: to the north the Red river 
and Rainy river whose waters uniting in lake Winnipeg are 
carried to Hudson bay through the Nelson; to the east the 
St. Lawrence system draining the five great lakes ; to the south 
the Mississippi, finally reaching the waters of the gulf of Mexi- 
co. The head waters of these river systems, instead of being 
in a high and mountainous district, occupy an area remark- 
ably low, and not a single mountain exists in the district. The 
highest altitude anywhere in Minnesota is less than twenty- 
three hundred feet above sea-level, while the average elevation 
of the watersheds is undoubtedly less than two thousand feet. 
The series of rock types which form the subject of this pa- 
per all come from the triangular area of Minnesota lying to 
the north of lake Superior, and to the east of the meridian of 
Duluth. This area forms a large part of one side of the 
great geosynclinal which is occupied by lake Superior. Near- 
ly every important rock type and formation existing on the 
north side of the lake are duplicated on the south side in Wis- 
consin and Michigan, and, in a general way, the succession 
of geological horizons from southeast to northwest found in 
Minnesota is repeated on the south side, but in reverse order. 
From lake Superior, on the northern side, the land rises rapid- 
*The borders of great Archean protaxis coincide very closely with 
the axes of several of the great American lakes, e. g., Great Slave, 
Great Bear, Winnipeg, and Superior; while the whole area is, in gen- 
eral, included quite accurately between the St. Lawrence, the Rainy, 
and the Mackenzie rivers. 
