Since this article in the _Quarterly Review_ was published, enormous sums of money have been spent on the Mississippi--partly with a view to the prevention of floods, but partly, also, to improve the river for the purposes of navigation. Placed in charge of a Mississippi Commission and of the Chief of Engineers in the United States Army, the river has been systematically surveyed; special studies and reports have been drawn up on every possible aspect of its normal or abnormal conditions and circumstances; the largest river dredges in the world have been employed to ensure an adequate depth of the river bed; engineering works in general on the most complete scale have been carried out--in fact, nothing that science, skill, or money could accomplish has been left undone. The difficulties were certainly considerable. There has always been a tendency for the river bed to get choked up by the sediment the stream failed to carry on; the banks are weak; while the variation in water level is sometimes as much as 10 feet in a single month. None the less, the Mississippi played for a time as important a rôle in the west and the south as the Erie Canal played in the north. Steamboats on the western rivers increased in number from 20, in 1818, to 1,200, in 1848, and there was a like development in flat boat tonnage. With the expansion of the river traffic came a growth of large cities and towns alongside. Louisville increased in population from 4,000, in 1820, to 43,000, in 1850, and St Louis from 4,900 to 77,000 in the same period.