The country is well watered, but with the exception of the Rufiji the rivers, save for a few miles from their mouths, are unnavigable. The largest streams are the Rovuma and Rufiji (q.v.), both rising in the central plateau and flowing to the Indian Ocean. Next in importance is the Pangani river, which, as stated above, has its head springs on the slopes of Kilimanjaro. Flowing in a south-easterly direction it reaches the sea after a course of some 250 m. The Wami and Kingani, smaller streams, have their origin in the mountainous region fringing the central plateau, and reach the ocean opposite the island of Zanzibar. Of inland river systems there are four—one draining to Victoria Nyanza, another to Tanganyika, a third to Nyasa and a fourth to Rukwa. Into Victoria Nyanza are emptied, on the east, the waters of the Mori and many smaller streams; on the west, the Kagera (q.v.), besides smaller rivers. Into Tanganyika flows the Malagarasi, a considerable river with many affluents, draining the west-central part of the plateau. The Kalambo river, a comparatively small stream near the southern end of Tanganyika, flows in a south-westerly direction. Not far from its mouth there is a magnificent fall, a large volume of water falling 600 ft. sheer over a rocky ledge of horse-shoe shape. Of the streams entering Nyasa the Songwe has been mentioned. The Ruhuhu, which enters Nyasa in 10° 30′ S., and its tributaries drain a considerable area west of 36° E. The chief feeders of Lake Rukwa are the Saisi and the Rupa-Songwe.
Mafia Island lies off the coast immediately north of 8° N. It has an area of 200 sq. m. The island is low and fertile, and extensively planted with coco-nut palms. It is continued southwards by an extensive reef, on which stands the chief village, Chobe, the residence of a few Arabs and Banyan traders. Chobe stands on a shallow creek almost inaccessible to shipping.
Geology.—The narrow foot-plateau of British East Africa broadens out to the south of Bagamoyo to a width of over 100 m. This is covered to a considerable extent by rocks of recent and late Tertiary ages. Older Tertiary rocks form the bluffs of Lindi. Cretaceous marls and limestones appear at intervals, extending in places to the edge of the upper plateau, and are extensively developed on the Makonde plateau. They are underlain by Jurassic rocks, from beneath which sandstones and shales yielding Glossopteris browniana var. indica, and therefore of Lower Karroo age, appear in the south but are overlapped on the north by Jurassic strata. The central plateau consists almost entirely of metamorphic rocks with extensive tracts of granite in Unyamwezi. In the vicinity of Lakes Nyasa and Tanganyika, sandstones and shales of Lower Karroo age and yielding seams of coal are considered to owe their position and preservation to being let down by rift faults into hollows of the crystalline rocks. In Karagwe certain quartzites, slates and schistose sandstones resemble the ancient gold-bearing rocks of South Africa.
The volcanic plateau of British East Africa extends over the boundary in the region of Kilimanjaro. Of the sister peaks, Kibo and Mawenzi, the latter is far the oldest and has been greatly denuded, while Kibo retains its crateriform shape intact. The rift-valley faults continue down the depression, marked by numerous volcanoes, in the region of the Natron Lake and Lake Manyara; while the steep walls of the deep depression of Tanganyika and Nyasa represent the western rift system at its maximum development.
Fossil remains of saurians of gigantic size have been found; one thigh bone measures 6 ft. 10 in., the same bone in the Diplodocus Carnegii measuring only 4 ft. 11 in.
Climate.—The warm currents setting landwards from the Indian Ocean bring both moisture and heat, so that the Swahili coast has a higher temperature and heavier rainfall than the Atlantic seaboard under the same parallels of latitude. The mean temperature on the west and east coasts of Africa is 72° and 80° Fahr. respectively, the average rainfall in Angola 36 in., in Dar-es-Salaam 60 in. On the Swahili coast the south-east monsoon begins in April and the north-east monsoon in November. In the interior April brings south-east winds, which continue until about the beginning of October. During the rest of the year changing winds prevail. These winds are charged with moisture, which they part with on ascending the precipitous side of the plateau. Rain comes with the south-east monsoon, and on the northern part of the coast the rainy season is divided into two parts, the great and the little Masika: the former falls in the months of September, October, November; the latter in February and March. In the interior the climate has a more continental character, and is subject to considerable changes of temperature; the rainy season sets in a little earlier the farther west and north the region, and is well marked, the rain beginning in November and ending in April; the rest of the year is dry. On the highest parts of the plateau the climate is almost European, the nights being sometimes exceedingly cold. Kilimanjaro has a climate of its own; the west and south sides of the mountain receive the greatest rainfall, while the east and north sides are dry nearly all the year. Malarial diseases are rather frequent, more so on the coast than farther inland. The Kilimanjaro region is said to enjoy immunity. Smallpox is frequent on the coast, but is diminishing before vaccination; other epidemic diseases are extremely rare.
Flora and Fauna.—The character of the vegetation varies with and depends on moisture, temperature and soil. On the low littoral zone the coast produced a rich tropical bush, in which the mangrove is very prominent. Coco-palms and mango trees have been planted in great numbers, and also many varieties of bananas. The bush is grouped in copses on meadows, which produce a coarse tall grass. The river banks are lined with belts of dense forest, in which useful timber occurs. The Hyphaene palm is frequent, as well as various kinds of gum-producing mimosas. The slopes of the plateau which face the rain-bringing monsoon are in some places covered with primeval forest, in which timber is plentiful. The silk-cotton tree (Bombax ceiba), miomba, tamarisk, copal tree (Hymenaea courbaril) are frequent, besides sycamores, banyan trees (Ficus indica) and the deleb palm (Borassus aethiopum). It is here we find the Landolphia florida, which yields the best rubber. The plateau is partly grass land without bush and forest, partly steppe covered with mimosa bush, which sometimes is almost impenetrable. Mount Kilimanjaro and Mount Meru exhibit on a vertical scale the various forms of vegetation which characterize East Africa (see [Kilimanjaro]).
East Africa is rich in all kinds of antelope, and the elephant, rhinoceros and hippopotamus are still plentiful in parts. Characteristic are the giraffe, the chimpanzee and the ostrich. Buffaloes and zebras occur in two or three varieties. Lions and leopards are found throughout the country. Crocodiles are numerous in all the larger rivers. Snakes, many venomous, abound. Of birds there are comparatively few on the steppe, but by rivers, lakes and swamps they are found in thousands. Locusts occasion much damage, and ants of various kinds are often a plague. The tsetse fly (Glossina morsitans) infests several districts; the sand-flea has been imported from the west coast. Land and water turtles are numerous.
Inhabitants.—On the coast and at the chief settlements inland are Arab and Indian immigrants, who are merchants and agriculturists. The Swahili (q.v.) are a mixed Bantu and Semitic race inhabiting the seaboard. The inhabitants of the interior may be divided into two classes, those namely of Bantu and those of Hamitic stock. What may be called the indigenous population consists of the older Bantu races. These tribes have been subject to the intrusion from the south of more recent Bantu folk, such as the Yao, belonging to the Ama-Zulu branch of the race, while from the north there has been an immigration of Hamito-Negroid peoples. Of these the Masai and Wakuafi are found in the region between Victoria Nyanza and Kilimanjaro. The Masai (q.v.) and allied tribes are nomads and cattle raisers. They are warlike, and live in square mud-plastered houses called tembe which can be easily fortified and defended. The Bantu tribes are in general peaceful agriculturists, though the Bantus of recent immigration retain the warlike instincts of the Zulus. The most important group of the Bantus is the Wanyamwezi (see [Unyamwezi]), divided into many tribes. They are spread over the central plains, and have for neighbours on the south-east, between Nyasa and the Rufiji, the warlike Wahehe. The Wangoni (Angoni), a branch of the Ama-Zulu, are widely spread over the central and Nyasa regions. Other well-known tribes are the Wasambara, who have given their name to the highlands between Kilimanjaro and the coast, and the Warundi, inhabiting the district between Tanganyika and the Kagera. In Karagwe, a region adjoining the south-west shores of Victoria Nyanza, the Bahima are the ruling caste. Formerly Karagwe under its Bahima kings was a powerful state. Many different dialects are spoken by the Bantu tribes, Swahili being the most widely known (see [Bantu Languages]). Their religion is the worship of spirits, ancestral and otherwise, accompanied by a vague and undefined belief in a Supreme Being, generally regarded as indifferent to the doings of the people.
The task of civilizing the natives is undertaken in various ways by the numerous Protestant and Roman Catholic missions established in the colony, and by the government. The slave trade has been abolished, and though domestic slavery is allowed, all children of slaves born after the 31st of December 1905 are free. For certain public works the Germans enforce a system of compulsory labour. Efforts are made by instruction in government and mission schools to spread a knowledge of the German language among the natives, in order to fit them for subordinate posts in administrative offices, such as the customs. Native chiefs in the interior are permitted to help in the administration of justice. The Mission du Sacré Cœur in Bagamoyo, the oldest mission in the colony, has trained many young negroes to be useful mechanics. The number of native Christians is small. The Moslems have vigorous and successful missions.