The Ohio river, as before hinted, differs from those just described, in the rapidity of its current, the width of its bed, the character of its channel, and in several other respects; but as its general character is well known, a few remarks in relation to it will here suffice. The obstructions to its navigation are sand-bars, some few rafts and mags, and rapids, to which the intricacy of its channel in several places may be added. During a middle and high stage of water, the obstructions entirely disappear, and an accelerated current is the only difficulty to be encountered. The average velocity of the current, in a moderate stage of water, may be estimated at two miles and a half, and in a high stage, at three miles per hour. The season in which the navigation of the Ohio can be relied on, commences between the middle of February and first of March, and continues to the latter part of June. A fall freshet usually takes place in October or November, and the river is again navigable for a few weeks. During the rest of the year, boats of inconsiderable burthen meet with numerous obstructions in their progress from the lowness of the water, and in many places no channel can be found of sufficient depth to admit their passage. At the distance of about seventeen miles from its mouth is the first serious obstruction to its navigation, consisting of a limestone bar extending across the river, denominated the Big Chain. Three miles above is another of a similar description. The range of rocks, of which these appear to be a portion, seems to extend across the point of land situated between the Ohio and Mississippi, presenting itself again on the latter, at the Big and Little Chains before mentioned. The falls of the Ohio at Louisville are impassable for boats of burthen, except in the higher stages of the water. Le Turt's Falls, and {261} numerous other rapids, denominated ripples, are also impassable for boats of heavy burthen when the river is at its lowest stages. In this state the river is fordable in numberless places. OF THE GREAT VALLEY OR BASIN OF THE MISSISSIPPI This vast region, embracing more than twenty degrees of latitude and about thirty of longitude, although it has been explored in various directions by men of intelligence, is yet but imperfectly known; and probably no country in the world affords a more ample or interesting field for philosophic investigation. A thorough acquaintance with its geological character would in all probability lead to the most important conclusions in forming a correct theory of the earth, while a knowledge of its vegetable and mineral productions may be conducive to the comforts and enjoyments of a large portion of the human family. All we shall presume to offer under this copious head, will be a few general remarks relative to the position and conformation of the valley, grounded almost exclusively upon the hydrography of the country, so far as it has come under our observation.