AFRICA
AFRICA, the name of a continent representing the largest of the three
great southward projections from the main mass of the earth's surface. It
includes within its remarkably regular outline an area, according to the
most recent computations, of 11,262,000 sq. m., excluding the islands.1
Separated from Europe by the Mediterranean Sea, it is joined to Asia at its
N.E. extremity by the Isthmus of Suez, 80 m. wide. From the most northerly
point, Ras ben Sakka, a little west of Cape Blanc, in 37 deg. 21' N., to
the most southerly point, Cape Agulhas, 34 deg. 51' 15'' S., is a distance
approximately of 5000 m.; from Cape Verde, 17 deg. 33' 22'' W., the
westernmost point, to Ras Hafun, 51 deg. 27' 52'' E., the most easterly
projection, is a distance (also approximately) of 4600 m. The length of
coast-line is 16,100 m. and the absence of deep indentations of the shore
is shown by the fact that Europe, which covers only 3,760,000 sq. m., has a
coast-line of 19,800 m.
I. PHYSICAL GEOGRAPHY
The main structural lines of the continent show both the east-to-west
direction characteristic, at least in the eastern hemisphere, of the more
northern parts of the world, and the north-to-south direction seen in the
southern peninsulas. Africa is thus composed of two segments at right
angles, the northern running from east to west, the southern from north to
south, the subordinate lines corresponding in the main to these two
directions.
Main Geographical Features.—The mean elevation of the continent
approximates closely to 2000 ft., which is roughly the elevation of both
North and South America, but is considerably less than that of Asia (3117
ft.). In contrast with the other continents it is marked by the
comparatively small area both of very high and of very low ground, lands
under 600 ft. occupying an unusually small part of the surface; while not
only are the highest elevations inferior to those of Asia and South
America, but the area of land over 10,000 ft. is also quite insignificant,
being represented almost entirely by individual peaks and mountain ranges.
Moderately elevated tablelands are thus the characteristic feature of the
continent, though the surface of these is broken by higher peaks and
ridges. (So prevalent are these isolated peaks and ridges that a special
term [Inselberg-landschaft] has been adopted in Germany to describe this
kind of country, which is thought to be in great part the result of wind
action.) As a general rule, the higher tablelands lie to the east and
south, while a progressive diminution in altitude towards the west and
north is observable. Apart from the lowlands and the Atlas range, the
continent may be divided into two regions of higher and lower plateaus, the
dividing line (somewhat concave to the north-west) running from the middle
of the Red Sea to about 6 deg. S. on the west coast. We thus obtain the
following four main divisions of the continent:—-(1) The coast plains—-
often fringed seawards by mangrove swamps—never stretching far from the
coast, except on the lower courses of streams. Recent alluvial flats are
found chiefly in the delta of the more important rivers. Elsewhere the
coast lowlands merely form the lowest steps of the system of terraces which
constitutes the ascent to the inner plateaus. (2) The Atlas range, which,
orographically, is distinct from the rest of the continent, being
unconnected with any other area of high ground, and separated from the rest
of the continent on the south by a depressed and desert area (the Sahara),
in places below sea-level. (3) The high southern and eastern plateaus,
rarely falling below 2000 ft., and having a mean elevation of about 3500
ft. (4) The north and west African plains, bordered and traversed by bands
of higher ground, but generally below 2000 ft. This division includes the
great desert of the Sahara.
The third and fourth divisions may be again subdivided. Thus the high
plateaus include:—(a) The South African plateau as far as about 12 deg. S.,
bounded east, west and south by bands of high ground which fall steeply to
the coasts. On this account South Africa has a general resemblance to an
inverted saucer. Due south the plateau rim is formed by three parallel
steps with level ground between them. The largest of these level areas, the
Great Karroo, is a dry, barren region, and a large tract of the plateau
proper is of a still more arid character and is known as the Kalahari
Desert. The South African plateau is connected towards the north-east with
(b) the East African plateau, with probably a slightly greater average
elevation, and marked by some distinct features. It is formed by a widening
out of the eastern axis of high ground, which becomes subdivided into a
number of zones running north and south and consisting in turn of ranges,
tablelands and depressions. The most striking feature is the existence of
two great lines of depression, due largely to the subsidence of whole
segments of the earth's crust, the lowest parts of which are occupied by
vast lakes. Towards the south the two lines converge and give place to one
great valley (occupied by Lake Nyasa), the southern part of which is less
distinctly due to rifting and subsidence than the rest of the system.
Farther north the western depression, sometimes known as the Central
African trough or Albertine rift-valley, is occupied for more than half its
length by water, forming the four lakes of Tanganyika, Kivu, Albert Edward
and Albert, the first-named over 400 m. long and the longest freshwater
lake in the world. Associated with these great valleys are a number of
volcanic peaks, the greatest of which occur on a meridional line east of
the eastern trough. The eastern depression, known as the East African
trough or rift-valley, contains much smaller lakes, many of them brackish
and without outlet, the only one comparable to those of the western trough
being Lake Rudolf or Basso Norok. At no great distance east of this rift-
valley are Kilimanjaro—with its two peaks Kibo and Mawenzi, the former
19,321 ft., and the culminating point of the whole continent—and Kenya
(17,007 ft.). Hardly less important is the Ruwenzori range (over 16,600
ft.), which lies east of the western trough. Other volcanic peaks rise from
the floor of the valleys, some of the Kirunga (Mfumbiro) group, north of
Lake Kivu, being still partially active. (c) The third division of the
higher region of Africa is formed by the Abyssinian highlands, a rugged
mass of mountains forming the largest continuous area of its altitude in
the whole continent, little of its surface falling below 5000 ft., while
the summits reach heights of 15,000 to 16,000 ft. This block of country
lies just west of the line of the great East African trough, the northern
continuation of which passes along its eastern escarpment as it runs up to
join the Red Sea. There is, however, in the centre a circular basin
occupied by Lake Tsana.
Both in the east and west of the continent the bordering highlands are
continued as strips of plateau parallel to the coast, the Abyssinian
mountains being continued northwards along the Red Sea coast by a series of
ridges reaching in places a height of 7000 ft. In the west the zone of high
land is broader but somewhat lower. The most mountainous districts lie
inland from the head of the Gulf of Guinea (Adamawa, &c.), where heights of
6000 to 8000 ft. are reached. Exactly at the head of the gulf the great
peak of the Cameroon, on a line of Volcanic action continued by the islands
to the south-west, has a height of 13,370 ft., while Clarence Peak, in
Fernando Po, the first of the line of islands, rises to over 9000. Towards
the extreme west the Futa Jallon highlands form an important diverging
point of rivers, but beyond this, as far as the Atlas chain, the elevated
rim of the continent is almost wanting.
The area between the east and west coast highlands, which north of 17
deg. N. is mainly desert, is divided into separate basins by other bands of
high ground, one of which runs nearly centrally through North Africa in a
line corresponding roughly with the curved axis of the continent as a
whole. The best marked of the basins so formed (the Congo basin) occupies a
circular area bisected by the equator, once probably the site of an inland
sea. The arid region, the Sahara—the largest desert in the world, covering
3,500,000 sq. m.—extends from the Atlantic to the Red Sea. Though generally
of slight elevation it contains mountain ranges with peaks rising to 8000
ft. Bordered N.W. by the Atlas range, to the N.E. a rocky plateau separates
it from the Mediterranean; this plateau gives place at the extreme east to
the delta of the Nile. That river (see below) pierces the desert without
modifying its character. The Atlas range, the north-westerly part of the
continent, between its seaward and landward heights encloses elevated
steppes in places 100 m. broad. From the inner slopes of the plateau
numerous wadis take a direction towards the Sahara. The greater part of
that now desert region is, indeed, furrowed by old water-channels.
The following table gives the approximate altitudes of the chief
mountains and lakes of the continent:—
Mountains. Ft. Lakes. Ft.
Rungwe (Nyasa) . 10,400 Chad . . . . 8502
Drakensberg . . 10,7002 Leopold II . . 1100
Lereko or Sattima . 13,2143 Rudolf . . . 1250
(Aberdare Range) Nyasa . . . 16453
Cameroon . . 13,370 Albert Nyanza . 20282
Elgon . . . 14,1523 Tanganyika . . 26243
Karissimbi . . Ngami . . . . 2950
(Mfumbiro) . 14,6833 Mweru . . . . 3000
Meru . . . 14,9553 Albert Edward . 30043
Taggharat (Atlas) . 15,0002 Bangweulu. . . 3700
Simen Mountains, . 15,1602 Victoria Nyanza. 37203
Abyssinia Abai . . . . 4200
Ruwenzori . . 16,6193 Kivu . . . . 48293
Kenya . . . 17,0073 Tsana . . . . 5690
Kilimanjaro . . 19,3213 Naivasha . . . 61353
The Hydrographic Systems.—-From the outer margin of the African plateaus
a large number of streams run to the sea with comparatively short courses,
while the larger rivers flow for long distances on the interior highlands
before breaking through the outer ranges. The main drainage of the
continent is to the north and west, or towards the basin of the Atlantic
Ocean. The high lake plateau of East Africa contains the head-waters of the
Nile and Congo: the former the longest, the latter the largest river of the
continent. The upper Nile receives its chief supplies from the mountainous
region adjoining the Central African trough in the neighbourhood of the
equator. Thence streams pour east to the Victoria Nyanza, the largest
African lake (covering over 26,000 sq. m.), and west and north to the
Albert Edward and Albert Nyanzas, to the latter of which the effluents of
the other two lakes add their waters. Issuing from it the Nile flows north,
and between 7 deg. and 10 deg. N. traverses a vast marshy level during
which its course is liable to blocking by floating 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
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