I cannot account for the great humidity of the watershed as compared with the rest of the country, but by the prevailing winds and the rains being from the south-east, and thus from the Indian Ocean:  with this wind generally on the surface one can observe an upper strong wind from the north-west, that is, from the low humid West Coast and Atlantic Ocean.  The double strata of winds can easily be observed when there are two sheets of clouds, or when burning grass over scores of square miles sends up smoke sufficiently high to be caught by the upper or north-west wind.  These winds probably meet during the heavy rains:  now in August they overlap each other.  The probability arises from all continued rains within the tropics coming in the opposite direction from the prevailing wind of the year.  Partial rains are usually from the south-east.

The direction of the prevailing wind of this region is well marked on the islands in Lake Bangweolo:  the trunks are bent away from the south-east, and the branches on that side are stunted or killed; while those on the north-west run out straight and make the trees appear lopsided.  The same bend away from the south-east is seen on all exposed situations, as in the trees covering the brow of a hill.  At Kizinga, which is higher than the Lake, the trees are covered with lichens, chiefly on the south-east sides, and on the upper surfaces of branches, running away horizontally to or from the north-west.  Plants and trees, which elsewhere in Africa grow only on the banks of streams and other damp localities, are seen flourishing all over the country:  the very rocks are covered with lichens, and their crevices with ferns.

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