MISSISSIPPI RIVER. This immense stream, form ing a river of the first order, deserves particular notice in an elementary work. Under the general term Mis sissippi, we include not only that river properly so call ed, but every secondary, or confluent body of water which enters into, or contributes to augment the mass of the main recipient.* Following this plan, the basin of the Mississippi may be naturally divided into four grand sections; first, ad vancing from east to west, the valley of Ohio and its tributary waters; that of Mississippi and its branches ; that of Missouri and its branches ; and that of the lower Mississippi, below the mouth of Missouri. Of these sections in order.
Ohio valley.—This very important region embraces about 200,000 square miles of area, equal to 128,000,000 of United States acres. Its greatest length is from the north-east sources of the Allegany river to the head of Bear creek, a branch of Tennessee river, 750 miles. Its greatest breadth, from the sources of the French Broad, to those of the Wabash river, 500 miles. In point of cli mate, it extends from N. Lat. 34° to 42° 30', or through seven and half degrees of latitude, affording a very con siderable difference of seasons and temperature.
It has been long the opinion of the author of this arti cle, an opinion formed from the fruits of many years ob servation, that the Ohio region once formed an immense inclined plane ; and that the beds of all the rivers have been formed by abrasion of water. This theory is sup ported by Mr. A. Bourne, author of a large and valu able map of the state of Ohio. The following is a quo tation from a manuscript letter from that gentleman on the subject. The hills are generally found near the rivers or large creeks, and parallel to them on each side; having between them the alluvial valley, through which the stream meanders, usually near the middle, but some times washes the foot of either hill alternately. Perhaps the best idea of the topography of this state, (Onto, which see,) by conceiving the state to be one vast ele vated plain, near the centre of which the streams rise, and in their course wear down a bed or valley, whose depth is in proportion to their size, or the density of the earth over which they flow. So that our hills, with some few
exceptions, are nothing more or less than cliffs or banks made by the action of the streams ; and although these cliffs or banks, on the rivers and larger creeks, approach the size of mountains, yet their tops are generally level, being the remains of the ancient plain. In the eastern part of the state, some few hills are found in sharp ridges similar to those in the eastern states. The base of the hills is generally composed of limestone, free, or sandstone, slate, and gravel, admixed with mineral coal, ochre, Sec." Bourne.
The author of this article surveyed, in 1815, Pittsburg and its environs, and found the rocks there, as in every other part of the Ohio valley, perfectly parallel to the horizon, of course, speaking technically, floetz forma tion. The circumstance most conclusive of the fact, that the hills and valleys of this region were formed by abrasion, is the uniformity of elevation and similar ma terial, of corresponding strata on the opposing banks of the streams; phenomena every where visible, where the nature of the country will admit accurate observation. The coal strata near Pittsburg are in every place found about 340 feet above low water level in the rivers of that vicinity.
Embracing the whole Ohio valley in one perspective, it is found divided into two very unequal portions by that river ; leaving 120,000 square miles to the south-east, and 80,000 on the north-west. The Ohio, forming a common recipient for the water of the minor streams of both slopes, flows in a very deep ravine, S. 64° NV., 478 geographical, or 543 miles in a direct line from Pitts burg to the junction of this river with the Mississippi. The entire length of Ohio by its meanders, is by actual admeasurement 948 miles.