10 



THE CABINET OF NATURAL HISTORY 



round the half of a circle, it is precipitated from the point 

 in a current, diagonally across its own channel, to another 

 curve of the same uniformity upon the opposite shore. 

 These curves are so regular, that the boatmen and Indians 

 calculate distances by them. Opposite to each of them, 

 there is alwaj'S a sand-bar, answering, in the convexity of 

 its form, to the concavity of "the bend," as it is called. 

 The river, by continually wearing these curves deeper, 

 returns, like many other streams before described, on its 

 own tract, so that a vessel, in some places, after sailing for 

 twenty-five or thirty miles, is brought round again to 

 within a mile of the place whence it started. When the 

 waters approach so near to each other, it often happens at 

 high floods, that they burst through the small tongue of 

 land; and, having insulated a portion, rush through what is 

 called the " cut off" with great velocity. At one spot, 

 called the "grand cut off," vessels now pass from one 

 point to another in half a mile, to a distance which it for- 

 merly required twenty miles to reach. After the flood 

 season, when the river subsides within its channel, it acts 

 with destructive force upon the alluvial banks, softened 

 and diluted by the recent overflow. Several acres at a 

 time, thickly covered with wood, are precipitated into 

 the stream; and the islands formed by the process before 

 described, lose large portions of their outer circumfer- 

 ence. 



Some years ago, when the Mississippi was regularly 

 surveyed, all its islands were numbered, from the conflu- 

 ence of the Missouri to the sea; but every season makes 

 such revolutions, not only in the number but in the magni- 

 tude and situation of these islands, that this enumeration is 

 now almost obsolete. Sometimes large islands are entirely 

 melted away — at other places they have attached them- 

 selves to the main shore, or, which is the more correct 

 statement, the interval has been filled up by myriads of 

 logs cemented together by mud and rubbish. When the 

 Mississippi and many of its great tributaries overflow their 

 banks, the waters, being no longer borne down by the 

 main current, and becoming impeded amongst the trees 

 and bushes, deposit the sediment of mud and sand with 

 which they are abundantly charged. Islands arrest the 

 progress of floating trees, and they become in this manner 

 reunited to the land; the rafts of trees, together with mud, 

 constituting at length a solid mass. The coarser portion 

 subsides first, and the most copious deposition is found 

 near the banks where the soil is most sandy. Finer par- 

 ticles are found at the farthest distances from the river, 

 where an impalpable mixture is deposited, forming a stiff 

 imctuous black soil. Hence the alluvions of these rivers 

 are highest directly on the banks, and slope back like a 

 natural "glacis" towards the rocky cliffs bounding the 



great valley. The Mississippi, therefore, by the continual 

 shifting of its course, sweeps away, during a great portion 

 of the j'ear, considerable tracts of alluvium which were 

 gradually accumulated by the overflow of former years, 

 and the matter now left during the spring-floods will be at 

 some future time removed. 



One of the most interesting features in this basin is " the 

 raft." The dimensions of this mass of timber were given 

 by Darby, in 1S16, as ten miles in length, about two 

 hundred and twenty yards wide, and eight feet deep, the 

 whole of which had accumulated, in consequence of some 

 obstruction, during about thirty-eight years, in an arm of 

 the Mississippi called the Atchafalaya, which is supposed 

 to have been at some past time a channel of the Red River, 

 before it intermingled its waters with the main stream. 

 This arm is in a direct line with the direction of the Mis- 

 sissippi, and it catches a large portion of the drift wood 

 annually brought down. The mass of timber in the raft is 

 continually increasing, and the whole rises and falls with 

 the water. Although floating, it is covered with green 

 bushes, like a tract of solid land, and its surface is enli- 

 vened in the autumn by a variety of beautiful flowers. 

 Notwithstanding the astonishing number of cubic feet of 

 timber collected here in so short a time, greater deposits 

 have been in progress at the extremity of the delta in the 

 Bay of Mexico. Unfortunately for the navigation of the 

 Mississippi, some of the largest trunks, after being cast 

 down from the position on which they grew, get their roots 

 entangled with the bottom of the river, where they remain 

 anchored, as it were, in the mud. The force of the current 

 naturally gives their tops a tendency downwards, and by 

 its flowing past, soon strips them of their leaves and 

 branches. These fixtures, called snags or planters, are 

 extremely dangerous to the steam-vessels proceeding up 

 the stream, in which they lie, like a lance in rest, con- 

 cealed beneath the water, with their sharp ends pointed 

 directly against the bow of vessels coming up. For the 

 most part these formidable snags remain so still, that they 

 can be detected only by a slight ripple above them, not 

 perceptible to inexperienced eyes. Sometimes, however, 

 they vibrate up and down, alternately showing their heads 

 above the surface and bathing them beneath it. So im- 

 minent is the danger caused by these obstructions, that 

 almost all the boats on the Mississippi are constructed on 

 a particular plan, to guard against fatal accidents. They 

 have at their bows, a place called a snag-chamber, and 

 confined only to boats calculated for the navigation of this 

 river; the chamber is partitioned off, about fifteen feet 

 from the stem, with very stout planks, well caulked, so 

 that the remainder of the vessel is completely cut off from 

 this room; and, consequently, should a snag strike the 



