VALLEY OP 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 



