WATER AS A GEOLOGICAL AGENT. 189 cannibals. It speaks well for the security felt in the country, and the rare appearance of beasts of prey, that all these compounds scattered in the wood are free from any disturbance, and the isolated huts, which have boards placed against the entrance, thus forming a door, need them chiefly for protection from the cool air of night.

Every step towards the south and west unfolded new pictures; splendid woodland scenery, swamps and jungles, where the overpowering beauty of the vegetable world concealed the difficulty of travel, zeribas and villages, clearings for new crops, banana plantations and yam-fields, streams and brooklets on every side. The country rose more and more when we had passed through Negunda, where Mbaga, Gambari’s brother, lives. Blocks of granite cropped out on the numerous hills, which must be regarded as the remains of ranges that have been washed away,and the paths down to the brooks gradually became steeper. It is curious to march through a narrow strip of steppe land, and become all of a sudden aware of a dark row of what appear to be dwarf trees lying on the ground, then, coming nearer, to find a descent of from sixty to a hundred feet, and the dwarfs changed into very giants, for they are rooted in the depths below, while only their tops are visible from the level of the plain. The frequent landslips also deserve mention. The farther one pushes in Monbuttu towards the west, that is, in the direction in which the country slopes, the deeper grows the stratum of reddish-brown mould which overlies the clay and the bare rock ; the more luxuriant, too, becomes the vegetation covering the ground, and the more rapidly proceeds the formation of humus produced by its decay. As this loose soil is, moreover, soaked with water throughout the year, small causes, such as the fall of a tree, are capable of producing a gap, and once a point of less resistance has been created, the erosive action of the water flowing towards it from all directions accomplishes the rest. If the water has once succeeded in forcing its way out, the original hole becomes transformed into a ravine, which grows wider and wider as the process of disintegration proceeds, and deeper and deeper, through the excavating action of the water flowing along its bottom. When vegetation has taken possession of the slopes, we have one of those innumerable threads of water with