In conducting this review, we may consider the basin subdivided into the four valleys already noticed ; that of Ohio, Mississippi Proper, Missouri, and Lower Missis sippi. The relative extent of each has been determined, and the principal streams noticed. If we were to turn an attentive eye to a map of those four sections, and un aided by a single fact drawn from actual observation, it would follow from theory, from its more southern position, and from its length extending east and west, that the valley of the Lower Mississippi must first discharge its waters ; the Ohio valley would follow ; Upper Missis sippi would succeed to Ohio; and lastly, would issue the discharge of Missouri, or largest subdivision of the basin: such are indeed the facts.
It would also be evident from inspection, that of every valley taken separately, nature opposes insurmountable obstacles to a simultaneous discharge. Red and Arkan saw rivers flow nearly parallel through fourteen degrees of longitude, and yet in every year the discharge of the former precedes that of the latter nearly a month. Red river is the true North American Nile, though on a smaller scale. That title has been bestowed on the Mississippi with unparalleled absurdity. Except in the single circumstance of each protruding a Delta at their respective mouths, no- two rivers could possibly present more contrasted features than does the Mississippi and Nile. In fact, except in one circumstance, very little resemblance exists between the Nile and Red river : the Nile in common years has only one flood, Red river has often two; but the floods of the Nile are discharged by regular rise and as regular depression, which is eminently the case with Red river ; a circumstance which, in a very sti iking manner, distinguishes both from the Mississippi, which rises and falls by pulsation, if such a term is ad missible.
Near the north-west angle of Louisiana, a chain of lakes commences on both shores of Red river, which continue to skirt that stream upwards 100 miles. The writer of this article examined these lakes, and found them to be evidently formed in the ancient channels and adjacent low grounds of considerable water-courses, the discharge or which, into Red river, has been gradually impeded by a natural embankment, formed by the sedi ment brought down by that river. These lakes, as they now exist, are from four or five, to thirty miles in length, and from one quarter to three miles wide, and are filled and emptied alternately, as the floods of Red river rise and fall : they are in fact real reservoirs, which in the rise of Red liver receive great part of its surplus water, and as the river depresses discharge that surplus slowly, tending very greatly to mitigate the rapid emission of the Red river flood on the Delta. As far as the writer
is informed, this feature is peculiar to Red river, and dis tinguishes that stream from every other.
Red river, like the Mississippi, has a flood in autumn, but what may be denominated the annual inundation of that river reaches the Delta in February, and continues through March and April.
The efflux of Arkansaw uniformly succeeds that of Red river ; but from the greater length of course, extent it drains, and also from the more northerly and moun tainous country from which its remote sources are drawn, the volume of the former very greatly exceeds that of the latter ; though from different causes, both rivers are alike in yielding their waters by a slow and regular discharge. The great mass of the flood of Arkansaw reaches the Delta in March and April, and is therefore simultaneous with the latter part of that of Red river. White river, in strictness, forms part of the Arkansaw tide, and flows out with the first flux of the latter stream.
We may here observe, that all the rivers of the Mis sissippi basin, above N. Lat. 37°, are liable to be an nually frozen. The Mississippi, at St. Louis, is three years in five passable on the ice with loaded carriages, by the first week in January. The Ohio, in an equal latitude, is not so soon frozen, though the cold is equally intense on the latter, as on the former river. The causes are obvious which produce this apparent anomaly. The waters of the Mississippi, flowing from high latitudes, arc cooled almost to the point of congelation, when they arrive at the junction of the Mississsippi and Missouri ; whilst those of Ohio, in the latitude of St. Louis, flowing nearly from east to west, demand a longer exposure to frost to become frozen. The gradual melting of the ice and snow above the latitude assumed, that of 37°, is another very controlling cause of the slow emission of the general flood.
The Ohio valley, from its compact form, greater com parative descent, and from the medium climate in which it is situated, emits its waters with more irregularity than any stream in the Mississippi basin. The Ohio tide of flood occurs from November until March, inclusive, though perhaps four years in five, this river yields the principal discharge in the latter month. The floods of this valley are more sudden in their rise, and more impetuous in their discharge, than that of any other section of the Mississippi basin. The main tide of Ohio reaches the Delta in May. The various streams are, however, so relatively placed, as to render a simul taneous discharge impossible. The effect, therefore, of this river, in producing an augmentation of the floods which inundate the Delta, is much lessened in its opera tion.