But that which demonstrates the humidity of the climate most strikingly is the number of earthen sponges or oozes met with. In going to Bangweolo from Kizinga, I crossed twenty-nine of these reservoirs in thirty miles of latitude, on a south-east course: this may give about one sponge for every two miles. The word "Bog" conveys much of the idea of these earthen sponges; but it is inseparably connected in our minds with peat, and these contain not a particle of peat, they consist of black porous earth, covered with a hard wiry grass, and a few other damp-loving plants. In many places the sponges hold large quantities of the oxide of iron, from the big patches of brown haematite that crop out everywhere, and streams of this oxide, as thick as treacle, are seen moving slowly along in the sponge-like small red glaciers. When one treads on the black earth of the sponge, though little or no water appears on the surface, it is frequently squirted up the limbs, and gives the idea of a sponge. In the paths that cross them, the earth readily becomes soft mud, but sinks rapidly to the bottom again, as if of great specific gravity: the water in them is always circulating and oozing. The places where the sponges are met with are slightly depressed valleys without trees or bushes, in a forest country where the grass being only a foot or fifteen inches high, and thickly planted, often looks like a beautiful glade in a gentleman's park in England. They are from a quarter of a mile to a mile broad, and from two to ten or more miles long. The water of the heavy rains soaks into the level forest lands: one never sees runnels leading it off, unless occasionally a footpath is turned to that use. The water, descending about eight feet, comes to a stratum of yellow sand, beneath which there is another stratum of fine white sand, which at its bottom cakes, so as to hold the water from sinking further.