Thence, including the headwaters of the Missouri, and taking direction southeasterly, dividing the tributaries of the Red River of the North from those of the Missouri to the source of the Minnesota; thence northeasterly, dividing the rivulets of the head lakes, Itasca, Cass, etc., from those confluent to the Red River of the North, separating the headwaters of the St. Croix from currents tributary to Lake Superior; thence embracing the confluent streams to the Mississippi in Wisconsin, Northern Illinois, and Indiana, to the Kankakee branch of the Illinois, say, 2,000
Thence, dividing the streams of the Lakes from those emptying into the Ohio as far as the extreme source of the Alleghany, say, 400
Thence along the dividing summit of the Atlantic slope to the source of the Tennessee; thence dividing the streams tending toward the Gulf, to the mouth of the Mississippi, and thence to starting point, say, 1,700 ______ Making an aggregate circuit of 6,100
Within this extensive limit we find, from surveys, the following aggregate area in square miles, estimated by valleys:
The valley of the Mississippi proper, 180,000
The valley of the Lower Mississippi, 330,000 _______ Total area, 1,210,000
As a natural consequence of the drainage of this immense area, the Mississippi receives into its waters a large amount of suspended earthy matter. This, however, does not very strikingly appear on the upper river, its own banks and those of its tributaries being more of a gravelly character and less friable than lower down. The gravity of particles, therefore, worn from the bed and sides of the channel above, unless the current be exceedingly strong, is greater than the buoyant capacity of the water, and falls to the bottom, along which, sometimes, it is forced by the abrasion of the water, until it meets some obstruction, which gathers the particles into shoal formations. This fact causes much inconvenience in the navigation of the upper rivers.
It is not until we reach the confluence of the streams of Southern Illinois and Missouri, that the sediment of the river becomes striking. Those streams, freighted with the rich loam and vegetable matter of the prairies of the east and west, soon change entirely the appearance of the Mississippi. Above the Missouri, the river is but slightly tinged; and indeed, after that great current enters, for some distance the two run side by side in the same channel, and yet are divided by a very distinct line of demarcation. It is only after the frequent sinuosities of the channel, that the two waters are thrown into each other and fairly blend. The sedimentary condition of the Missouri is so great that drift floating upon its muddy surface, by accretion becomes so heavily laden with earthy matter that it sinks to the bottom. This precipitation of drift has taken place to such an extent, that the bed of the Missouri is in many places completely covered to a great depth by immense fields of logs. Of all the silt thrown into the Mississippi, the Missouri furnishes about one third.