I.AKE EIKWA. 807 displaced. The alluvial deposits, incessantly disturbed by the current, presents every year a fresh system of ramifying channels, while seawards the outlines of the coast are continually modified by the ceaseless action of the coral-building polyps. In proportion to the size of its basin, the Rufiji delta is very extensive, developing a coastline about 54 miles long and covering a total superficial area of no less than GOO square miles. It is intersected by about a dozen so-cuUod mtoH, or estuaries, some of which are not in constant communication with the fluvial system, although connected with it for the greater part of the year, when the sweet and saline waters are intermingled in their channels. The largest volumes of the fluvial current are discharged through the northern branches, the Bumba or Msala, the Kiomboni, Siinba-Uranga, and Kibunya, and these are consequently the most accessible to shipping, which is able to ascend them at high water. The Simba-Uranga mouth especially is much frequented by coasters, which come to load timber on the banks of the river. All the channels in the neighbourhood of the sea are fringed by dense mangrove thickets, and here the few habitations of the natives are raised on piles sunk in the mud. Higher up, where the .'^oil is less saturated with moisture, no more trees arc seen, and the ground is covered with tall grasses, yielding where cultivated rich crops of rice. Compared with the Rufiji, the other streams discharging into the Zanzibar waters are of inconsiderable size. The Kingani, which Holm wood ascended for a distance of 120 miles from its mouth, is also known as the Mto, Mbazi, or Rufu (Ru-Fu), names which have all the same meaning of '* river." It has its source in the valleys of the eastern slope east of the Usagara uplands. The Waini, which also reaches the coast opposite the island of Zanzibar, but a little farther north, collects its first waters much farther west in the hills skirting the plateau. •' Lake Rikwa. But the space comprised between the basins of these rivers and those flowing to Tanganyika is dotted over with shallow flooded depressions without any out- flow. The largest of these reservoirs, lying west of the heights where the main branches of the Rufigi have their origin, is Ijake Rikwa (Likwa, Ilikwa), which was discovered by Thomson in 1880, and has since been visited by Cotterill and Kaiser. Seen from the summit of the Liambu ^lountains enclosing it on the north- west, and separating it from Tanganyika, Rikwa appears to fill a regular valley disposed north-east and south-west parallel with the axis of Tanganyika and Xyassa, and forming part of the same lacustrine system in the continental relief. It stands at an estimated altitude of nearly 2,600 feet, that is to say, about 100 feet above the level of Tanganyika, and has a probable length of about 60 miles, with a breadth varying from 10 to 20 mihs. Rikwa receives several affluents at both extremities, including even a considerable stream, the Katuma or Mkafu, which takes its rise north of Karema, in the mountains skirting the great lake. But all these contributions of fresh water, being carried off by the evaporation of the
