vegetation. After receiving the Bahr-el-Ghazal from the
west and the Sobat, Blue Nile and Atbara from the Abyssinian
highlands (the chief gathering ground of the flood-water),
it crosses the great desert and enters the Mediterranean by
a vast delta. The most remote head-stream of the Congo is
the Chambezi, which flows south-west into the marshy Lake
Bangweulu. From this lake issues the Congo, known in its
upper course by various names. Flowing first south, it
afterwards turns north through Lake Mweru and descends to the
forest-clad basin of west equatorial Africa. Traversing this
in a majestic northward curve and receiving vast supplies of
water from many great tributaries, it finally turns south-west
and cuts a way to the Atlantic Ocean through the western
highlands. North of the Congo basin and separated from it
by a broad undulation of the surface is the basin of Lake
Chad---a flat-shored, shallow lake filled principally by the
Shad coming from the south-east. West of this is the basin
of the Niger, the third river of Africa, which, though flowing
to the Atlantic, has its principal source in the far west,
and reverses the direction of flow exhibited by the Nile and
Congo. An important branch, however--the Benue--comes from the
south-east. These four river-basins occupy the greater part
of the lower plateaus of North and West Africa, the remainder
consisting of arid regions watered only by intermittent streams
which do not reach the sea. Of the remaining rivers of the
Atlantic basin the Orange, in the extreme south, brings the
drainage from the Drakensberg on the opposite side of the
continent, while the Kunene, Kwanza, Ogowe and Sanaga drain
the west corst highlands of the southern limb; the Volta,
Komoe, Bandama, Gambia and Senegal the highlands of the western
limb. North of the Senegal for over 1000 m. of coast the
arid region reaches to the Atlantic. Farther north are the
streams, with comparatively short courses, which reach
the Atlantic and Mediterranean from the Atlas mountains.
Of the rivers flowing to the Indian Ocean the only one draining
any large part of the interior plateaus is the Zambezi,
whose western branches rise in the west coast highlands.
The main stream has its rise in 11 deg. 21' 3'' S. 24 deg. 22' E.
at an elevation of 5000 ft. It flows west and south for a
considerable distance before turning to the east. All the
largest tributaries, including the Shire, the outflow of Lake
Nyasa, flow down the southern slopes of the band of high ground
which stretches across the conbnent in 10 deg. to 12 deg. S. In
the south-west the Zambezi system interlaces with that of the
Taukhe (or Tioghe), from which it at times receives surplus
water. The rest of the water of the Taukhe, known in its
middle course as the Okavango, is lost in a system of swamps
and saltpans which formerly centred in Lake Ngami, now dried
up. Farther south the Limpopo drains a portion of the
interior plateau but breaks through the bounding highlands
on the side of the continent nearest its source. The Rovuma,
Rufiji, Tana, Juba and Webi Shebeli principally drain the
outer slopes of the East African highlands, the last named
losing itself in the sands in close proximity to the sea.
Another large stream, the Hawash, rising in the Abyssinian
mountains, is lost in a saline depression near the Gulf of
Aden. Lastly, between the basins of the Atlantic and Indian
Oceans there is an area of inland drainage along the centre
of the East African plateau, directed chiefly into the lakes
in the great rift-valley. The largest river is the Omo,
which, fed by the rains of the Abyssinian highlands, carries
down a large body of water into Lake Rudolf. The rivers
of Africa are generally obstructed either by bars at their
mouths or by cataracts at no great distance up-stream.
But when these obstacles have been overcome the rivers and
lakes afford a network of navigable waters of vast extent.
The calculation of the areas of African drainage systems,
made by Dr A. Bludau (Petermanns Mitteilungen, 43,
1897, pp. 184-186) gives the following general results:--
Basin of the Atlantic . . . . . 4,070,000 sq. m.
'' '' Mediterranean . . . 1,680,000 ''
'' '' Indian Ocean . . . . 2,086,000 ''
Inland drainage area . . . . . 3,452,000 ''
The areas of individual river-basins are:--
Congo (length over 3000 m.) . . 1,425,000 sq. m.
Nile ( '' fully 4000 m.) . . 1,082,0004 ''
Niger ( '' about 2600 m.) . . 808,0005 ''
Zambezi ( '' '' 2000 m.) . . 513,500 ''
Lake Chad . . . . . . . . . 394,000 ''
Orange (length about 1300 m.) . . 370,505 ''
'' (actual drainage area) . . 172,500 ''
The area of the Congo basin is greater than that of any
other river except the Amazon, while the African inland
drainage area is greater than that of any continent but
Asia, in which the corresponding area is 4,000,000 sq. m.
The principal African lakes have been mentioned in the description
of the East African plateau, but some of the phenomena connected
with them may be spoken of more particularly here. As a rule
the lakes which occupy portions of the great rift-valleys have
steep sides and are very deep. This is the case with the two
largest of the type, Tanganyika and Nyasa, the latter of which
has depths of 430 fathoms. Others, however, are shallow,
and hardly, reach the steep sides of the valleys in the dry
season. Such are Lake Rukwa, in a subsidiary depression north
of Nyasa, and Eiassi and Manyara in the system of the eastern
rift-valley. Lakes of the broad type are of moderate depth,
the deepest sounding in Victoria Nyanza being under 50
fathoms. Apart from the seasonal variations of level, most
of the lakes show periodic fluctuations, while a progressive
desiccation of the whole region is said to be traceable,
tending to the ultimate disappearance of the lakes. Such a
drying up has been in progress during long geologic ages, but
doubt exists as to its practical importance at the present
time. The periodic fluctuations in the level of Lake Tanganyika
are such that its outllow is intermittent. Besides the East
African lakes the principal are:---Lake Chad, in the northern
area of inland drainage; Bangweulu and Mweru, traversed by the
head-stream of the Congo; and Leopold II. and Ntomba (Mantumba),
within the great bend of that river. All, exceot possibly
Mweru, are more or less shallow, and Chad appears to by drying
up. The altitudes of the African lakes have already been stated.
Divergent opinions have been beld as to the mode of origin
of the East African lakes, especially Tanganyika, which some
geologists have considered to represent an old arm of the
sea, dating from a time when the whole central Congo basin
was under water; others holding that the lake water has
accumulated in a depression caused by subsidence. The former
view is based on the existence in the lake of organisms
of a decidedly marine type. They include a jelly-fish,
molluscs, prawns, crabs, &c., and were at first considered
to form an isolated group found in no other of the African
lakes; but this supposition has been proved to be erroneous.
Islands.--With one exception---Madagascar--the African islands
are small. Madagascar, with an area of 229,820 sq. m., is,
after New Guinea and Borneo, the largest island of the world.
It lies off the S.E. coast of the continent, from which
it is separated by the deep Mozambique channel, 250 m.
wide at its narrowest point. Madagascar in its general
structure, as in flora and fauna, forms a connecting link
between Africa and southern Asia. East of Madagascar are
the small islands of Mauritius and Reunion. Sokotra lies
E.N.E. of Cape Guardafui. Off the north-west coast are
the Canary and Cape Verde archipelagoes. which, like some
small islands in the Gulf of Guinea, are of volcanic origin.
Climate and Health.---Lying almost entirely within the
tropics, and equally to north and south of the equator,
Africa does not show excessive variations of temperature.
Great heat is experienced in the lower plains and desert
regions of North Africa, removed by the great width of the
continent from the influence of the ocean, and here, too,
the contrast between day and night, and between summer and
winter, is greatest. (The rarity of the air and the great
radiation during the night cause the temperature in the Sahara
to fall occasionally to freezing point.) Farther south, the
heat is to some extent modified by the moisture brought from
the ocean, and by the greater elevation of a large part of
the surface, especially in East Africa, where the range of
temperature is wider than in the Congo basin or on the Guinea
coast. In the extreme north and south the climate is a warm
temperate one, the northern countries being on the whole
hotter and drier than those in the southern zone; the south
of the continent being narrower than the north, the influence
of the surrounding ocean is more felt. The most important
climatic differences are due to variations in the amount of
rainfall. The wide heated plains of the Sahara, and in a
lesser degree the corresponding zone of the Kalahari in the
south, have an exceedingly scanty rainfall, the winds which
blow over them from the ocean losing part of their moisture
as they pass over the outer highlands, and becoming constantly
drier owing to the heating effects of the burning soil of the
interior; while the scarcity of mountain ranges in the more
central parts likewise tends to prevent condensation. In
the inter-tropical zone of summer precipitation, the rainfall
is greatest when the sun is vertical or soon after. It is
therefore greatest of all near the equator, where the sun is
twice vertical, and less in the direction of both tropics.
The rainfall zones are, however, somewhat deflected from a
due west-to-east direction, the drier northern conditions
extending southwards along the east coast, and those of the
south northwards along the west. Within the equatorial zone
certain areas, especially on the shores of the Gulf of Guinea
and in the upper Nile basin, have an intensified rainfall,
but this rarely approaches that of the rainiest regions of the
world. The rainiest district in all Africa is a strip of
coastland west of Mount Cameroon, where there is a mean
annual rainfall of about 390 in. as compared with a mean of
458 in. at Cherrapunji, in Assam. The two distinct rainy
seasons of the equatorial zone, where the sun is vertical at
half-yearly intervals, become gradually merged into one in
the direction of the tropics, where the sun is overhead but
once. Snow falls on all the higher mountain ranges, and on
the highest the climate is thoroughly Alpine. The countries
bordering the Sahara are much exposed to a very dry wind, full
of fine particles of sand, blowing from the desert towards the
sea. Known in Egypt as the khamsin, on the Mediterranean as the
sirocco, it is called on the Guinea coast the harmattan. This
wind is not invariably hot; its great dryness causes so much
evaporation that cold is not infrequently the result. Similar
dry winds blow from the Kalahari in the south. On the eastern
coast the monsoons of the Indian Ocean are regularly felt,
and on the south-east hurricanes are occasionally experienced.
While the climate of the north and south, especially the south,
is eminently healthy, and even the intensely heated Sahara is
salubrious by reason of its dryness, the tropical zone as a
