VALLEY OF THE MINNESOTA RIVER. 573 
lake of the Pomme de Terre stands at a level of about 1,340 
feet. The Leaf hills are in part drained towards the south- 
west by the Chippewa river and in part towards the northwest 
by the Red river of the North. Some of these hills reach the 
altitude given above, of 1,750 feet. On the other side of the 
Minnesota basin, more than one hundred and twenty-five miles 
to the southwest, lies the Coteau des Prairies, forming the 
southwestern boundary of the valley and reaching at different 
points an elevation of from 1,900 to 1,950 feet above the level 
of the sea. Lake Benton which is the head lake of the Red- 
wood river lies at an elevation of 1,754 feet above the sea level. 
From these extremes of elevation northwestward, westward 
and southwestward, the basin inclines gently toward the east. 
At low water the mouth of the Minnesota river, where it dis- 
charges its waters into the Mississippi at Fort Snelling, lies 
at an altitude of 688 feet above sea level and the flood-plane at 
this point is 710 feet. In Hennepin county some of the lands 
drained by Nine Mile creek, which empties from the north into 
the Minnesota, near its mouth, lie at an altitude of about 1,000 
feet, while just across the basin, in Dakota county, the south- 
ern edge attains in places an altitude of about 1,100 feet. 
Character of the basin. The main stream of the basin— 
the Minnesota river—from the head of Big Stone lake to Fort 
Snelling, runs in a gorge varying in width from half a mile to 
four miles, and about 230 miles in length. The sides of this 
gorge rise, with slopes of from twenty to forty degrees, to 
from one hundred to two hundred and thirty feet above the 
level of the river, and to the general country level. The river 
itself is nowhere a large stream and except at a few points 
does not wash the bases of its bluffs, but flows in a trench 
through alluvial deposits. From the edges of this trench 
level country, diversified with many ponds, extends to the 
bases of the bluffs, broken in many places by exposures of 
gneissic and gabbroid rocks. Not far from the town of Morton, 
a notable diabasic dyke, 175 feet wide, cuts across the gorge. 
Besides this very large dyke there are upwards of twenty 
others in the region of the crystalline rocks. In general there 
are few exposures of rock below the town of Beaver Falls, but 
above this point the whole floor of the gorge is often broken 
for miles with the outcrops. 
The average width of the Minnesota valley is not far from 
100 miles. On the north it extends among the morainic hills 
of the belt which stretches from Lake Minnetonka to Otter 
