Page:The empire and the century.djvu/830

a sea of reeds and a waste of water. For nearly 800 miles the Bahr-el-Gebel wanders between hedges of tall papyrus, much of which stands quite 15 feet above the river surface. Occasionally a palm-tree or a stunted mimosa is visible in the far distance, indicating the existence of a dry patch of land; but such objects only intensify the general flatness. The 'sudd' blocks form obstacles of a most serious nature, and if not cleared away as soon as they form close the river altogether. These blocks are chiefly caused by the breaking loose during stormy weather of large areas of the reeds, which find a nursery in the shallow lagoons so common in this locality. These water-plants, mainly consisting of papyrus and two varieties of tall grasses, grow in the beds of the lagoons. The attachment of their roots, however, is not a very stable one, and in strong winds, especially if accompanied by a rise in the water levels, they become easily detached. The result is a floating island, formed by a mass of vegetation, closely bound together by creeping plants, and by the earth which still adheres to the roots of the larger reeds. Should such an island drift into the river channel, it is carried along by the stream until it reaches a sharp bend or a narrow point, when it comes to an anchor. Other islands of the same nature probably follow it, and are similarly arrested, the area of the original obstruction being by this means enlarged. By the pressure thus caused, the floating mass is gradually compressed into a smaller space, its thickness below water being consequently augmented, and the waterway beneath it proportionately diminished. This necessarily causes an increased velocity in the contracted water section, and as fresh portions of 'sudd' float down the stream they are sucked below the surface, and so tend still further to add to the thickness of the obstacle. With each fresh addition the area of the waterway is diminished, and the compression increases until the entire mass becomes wedged into a solid block of crushed reeds and earth, sometimes as much as