Another characteristic feature of the adjacent bottom lands are the countless crescent-shaped lakes, oxbows, as they are called, which line the river on either side. but are partly or wholly separated from it. These arc formed by cut-offs. The river flows in great curves, which constantly tend to increase in diameter. Thus they en croach on one another, and filially at flood-time, when the impact of the current becomes strong est. cut through the narrow neck separating adjacent curves, thus shortening the course, and leaving the loop as a crescent-shaped lake.
hielow the mouth of Red River, the Mississippi divides into branches, the -Atchafalaya, Plaque mine, and Lafourche bayous being examples of such distributaries. In the lowlands near its mouth below New Orleans it divides still further, entering the Gulf by means of several passages known as passes, the principal of which are the Southwest and South Passes and the Pass it l'Outrc. At the mouth of each of these passes, except the South Pass, where jetties have been built to prevent it, is a bar formed by the deposit of silt from the river on meeting the quiet waters of the Gulf. The quantity of sediment brought down by the river is enormous, being below the Missouri .0035 of the volume of water, which
latter amounts to 145 cubic miles per annum. The area of the delta of the river is estimated at over 12.000 square miles. It is everywhere threaded with interlacing bayous and navigable channels, placing every cultivable acre of its lands near to steamboat navigation, one-tenth of the land being estimated as taken up by such water surfaces o• channels. The timber in the delta region is mostly sycamore, cypress, and oak—the sycamore margining the streams, the cypress occupying the swamps. and the oaks the lands not liable to frequent inundation.
The climate of the Mississippi Valley ranges from semi-aretie to semi•tropieal. At the Falls of Saint Anthony, and above, spirit thermometers must he employed to register the extreme low temperature in winter, which often touches 40° F. below zero; and yet the extreme of summer heat is but a few degrees less at Saint Paul than at New Orleans. 97° to 104°. The range between the extremes is about (15° more at the source than at the mouth of the river. The annual mean temperature at New Orleans is 69° ; at Cairo, 45°.