to a mile (100 mm/km). The length of the river itself, from the Ohio mouth to the Gulf is about due to its windings. Its mean fall is about 3 inches per mile (50 mm/km). On account of the rapid deposition of sediment near the main channel at times of overflow, the flood plain, as is normally the case on mature valley floors, has a lateral slope of as much as 5, 10, or even in the first mile from the river, but this soon decreases to a less amount. Thus just a short distance from the river, the flood plain is often swampy, unless its surface is there aggraded by the tributary streams. For this reason Louisiana, Arkansas and Mississippi rank immediately after Florida in swamp area. The great river receives an abundant load of silt from its tributaries, and takes up and lays down silt from its own bed and banks with every change of velocity. The swiftest current follows the outer side of every significant curve in the channel. Thus the concave bank on the side of the fastest part of the river is worn away. Any chance irregularity is exaggerated, and in time a series of large serpentines or meanders is developed, the most-symmetrical examples at present being those near Greenville, Mississippi. The growth of the meanders tends to give the river continually increasing length. This tendency is counteracted by the sudden occurrence of cut-offs from time to time, so that a fairly constant length is maintained. The floods of the Mississippi usually occur in spring or summer. Owing to the great size of the drainage basin, it seldom happens that the three upper tributaries are simultaneously flooded. It is a serious problem for the lower river if two of the large tributaries flood at the same time. In this case, the lower river will rise to 30, 40 or even . The fall of the river is significantly steepened and its velocity is accelerated down stream from the point of highest rise. Conversely, the fall and the velocity are both diminished up stream from the same point. The load of silt carried down stream by the river finally, after many halts on the way, reaches the waters of the Gulf. There, the decrease of velocity aided by the salinity of the sea water, causes the formation of a remarkable delta, leaving less aggraded areas as