Africa

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 whole is, for European races,

the most unhealthy portion of the world. This is especially the case in the

lower and moister regions, such as the west coast, where malarial fever is

very prevalent and deadly; the most unfavourable factors being humidity

with absence of climatic variation (daily or seasonal). The higher

plateaus, where not only is the average temperature lower, but such

variations are more extensive, are more healthy; and in certain localities

(e.g. Abyssinia and parts of British East Africa) Europeans find the

climate suitable for permanent residence. On tablelands over 6500 ft. above

the sea, frost is not uncommon at night, even in places directly under the

equator. The acclimatization of white men in tropical Africa generally is

dependent largely on the successful treatment of tropical diseases.

Districts which had been notoriously deadly to Europeans were rendered

comparatively healthy after the discovery, in 1899, of the species of

mosquito which propagates malarial fever, and the measures thereafter taken

for its destruction and the filling up of swamps. The rate of mortality

among the natives from tropical diseases is also high, one of the most

fatal being that known as sleeping sickness. (The ravages of this disease,

which also attacks Europeans, reached alarming proportions between 1893 and

1907, and in the last-named year an international conference was held in

London to consider measures to combat it.) When removed to colder regions

natives of the equatorial districts suffer greatly from chest complaints.

Smallpox also makes great ravages among the negro population.

Flora.—The vegetation of Africa follows very closely the distribution of

heat and moisture. The northern and southern temperate zones have a flora

distinct from that of the continent generally, which is tropical. In the

countries bordering the Mediterranean are groves of oranges and olive

trees, evergreen oaks, cork trees and pines, intermixed with cypresses,

myrtles, arbutus and fragrant tree-heaths. South of the Atlas range the

conditions alter. The zones of minimum rainfall have a very scanty flora,

consisting of plants adapted to resist the great dryness. Characteristic of

the Sahara is the date-palm, which flourishes where other vegetation can

scarcely maintain existence, while in the semidesert regions the acacia

(whence is obtained gum-arabic) is abundant. The more humid regions have a

richer vegetation —dense forest where the rainfall is greatest and

variations of temperature least, conditions found chiefly on the tropical

coasts, and in the west African equatorial basin with its extension towards

the upper Nile; and savanna interspersed with trees on the greater part of

the plateaus, passing as the desert regions are approached into a scrub

vegetation consisting of thorny acacias, &c. Forests also occur on the

humid slopes of mountain ranges up to a certain elevation. In the coast

regions the typical tree is the mangrove, which flourishes wherever the

soil is of a swamp character. The dense forests of West Africa contain, in

addition to a great variety of dicotyledonous trees, two palms, the Elaeis

guincensis (oil-palm) and Raphia vinifera (bamboo-palm), not found,

generally speaking, in the savanna regions. The bombax or silk-cotton tree

attains gigantic proportions in the forests, which are the home of the

indiarubber-producing plants and of many valuable kinds of timber trees,

such as odum (Chlorophora excelsa), ebony, mahogany (Khaya senegalensis),

African teak or oak (Oldfieldia africana) and camwood (Baphia nitida.) The

climbing plants in the tropical forests are exceedingly luxuriant and the

undergrowth or ``bush'' is extremely dense. In the savannas the most

characteristic trees are the monkey bread tree or baobab (Adanisonia

digitata), doom palm (Hyphaene) and euphorbias. The coffee plant grows wild

in such widely separated places as Liberia and southern Abyssinia. The

higher mountains have a special flora showing close agreement over wide

intervals of space, as well as affinities with the mountain flora of the

eastern Mediterranean, the Himalayas and Indo-China (cf. A. Engler, Uber

die Hochgebirgsflora des tropischen Afrika, 1892).

In the swamp regions of north-east Africa the papyrus and associated

plants, including the soft-wooded ambach, flourish in immense quantities—-

and little else is found in the way of vegetation. South Africa is largely

destitute of forest save in the lower valleys and coast regions. Tropical

flora disappears, and in the semi-desert plains the fleshy, leafless,

contorted species of kapsias, mesembryanthemums, aloes and other succulent

plants make their appearance. There are, too, valuable timber trees, such

as the yellow pine (Podocarpus elongatus), stinkwood (Ocotea), sneezewood

or Cape ebony (Pteroxylon utile) and ironwood. Extensive miniature woods of

heaths are found in almost endless variety and covered throughout the

greater part of the year with innumerable blossoms in which red is very

prevalent. Of the grasses of Africa alfa is very abundant in the plateaus

of the Atlas range.

Fauna.—The fauna again shows the effect of the characteristics of the

vegetation. The open savannas are the home of large ungulates, especially

antelopes, the giraffe (peculiar to Africa), zebra, buffalo, wild ass and

four species of rhinoceros; and of carnivores, such as the lion, leopard,

hyaena, &c. The okapi (a genus restricted to Africa) is found only in the

dense forests of the Congo basin. Bears are confined to the Atlas region,

wolves and foxes to North Africa. The elephant (though its range has become

restricted through the attacks of hunters) is found both in the savannas

and forest regions, the latter being otherwise poor in large game, though

the special habitat of the chimpanzee and gorilla. Baboons and mandrills,

with few exceptions, are peculiar to Africa. The single-humped camel—as a

domestic animal—is especially characteristic of the northern deserts and

steppes.

The rivers in the tropical zone abound with hippopotami and crocodiles,

the former entirely confined to Africa. The vast herds of game, formerly so

characteristic of many parts of Africa, have much diminished with the

increase of intercourse with the interior. Game reserves have, however,

been established in South Africa, British Central Africa, British East

Africa, Somahland, &c., while measures for the protection of wild animals

were laid down in an international convention signed in May 1900.

The ornithology of northern Affica presents a close resemblance to that

of southern Europe, scarcely a species being found which does not also

occur in the other countries bordering the Mediterranean. Among the birds

most characteristic of Africa are the ostrich and the secretary-bird. The

ostrich is widely dispersed, but is found chiefly in the desert and steppe

regions. The secretary-bird is common in the south. The weaver birds and

their allies, including the long-tailed whydahs, are abundant, as are,

among game-birds, the francolin and guinea-fowl. Nany of the smaller birds,

such as the sun-birds, bee-eaters, the parrots and halcyons, as well as the

larger plantain-eaters, are noted for the brilliance of their plumage. Of

reptiles the lizard and chameleon are common, and there are a number of

venomous serpents, though these are not so numerous as in other tropical

countries. The scorpion is abundant. Of insects Africa has many thousand

different kinds; of these the locust is the proverbial scourge of the

continent, and the ravages of the termites or white ants are almost

incredible. The spread of malaria by means of mosquitoes has already been

mentioned. The tsetse fly, whose bite is fatal to all domestic animals, is

common in many districts of South and East Africa. Fortunately it is found

nowhere outside Africa. (E. HE.; F. R. C.)

1 With the islands, 11,498,000 sq. m.

2 Estimated.

3 See the calculations of Capt. T. T. Behrens, Geog. Journal, vol. xxix.

(1907).

4 The estimate of Capt. H. G. Lyons in 1905 was 1,107,227 sq. mi.

5 including waterless tracts naturally belonging to the river-basin.

II. GEOLOGY

In shape and general geological structure Africa bears a close

resemblance to India. Both possess a meridional extension with a broad east

and west folded region in the north. In both a successive series of

continental deposits, ranging from the Carboniferous to the Rhaetic, rests

on an older base of crystalline rocks. In the words of Professor Suess,

``India and Africa are true plateau countries.''

Of the primitive axes of Africa few traces remain. Both on the east and

west a broad zone of crystalline rochs extends parallel with the coast-line

to form the margin of the elevated plateau of the interior. Occasionally

the crystalline belt comes to the coast, but it is usually reached by two

steps known as the coastal belt and foot-plateau. On the flanks of the

primitive western axis certain ancient sedimentary strata are thrown into

folds which were completed before the commencement of the mesozoic period.

In the south, the later palaeozoic rocks are also thrown into acute folds

by a movement acting from the south, and which ceased towards the close of

the mesozoic period. In northern Africa the folded region of the Atlas

belongs to the comparatively recent date of the Alpine system. None of

these earth movements affected the interior, for here the continental

mesozoic deposits rest, undisturbed by folding, on the primary sedimentary

and crystalline rocks. The crystalline massif, therefore, presents a solid

block which has remained elevated since early palaeozoic times, and against

which earth waves of several geological periods have broken.

The formations older than the mesozoic are remarkably unfossiliferous, so

that the determination of their age is frequently a matter of speculation,

and in the following table the European equivalents of the pre-Karroo

formations in many regions must be regarded as subject to considerable

revision.

Rocks of Archean age cover wide areas in the interior, in West and East

Africa and across the Sahara. Along the coastal margins they underlie the

newer formations and appear in the deep valleys and kloofs wherever

denudation has laid them bare. The prevailing types are granites, gneisses

and schists. In the central regions the predominant strike of the fohae is

north and south. The rocks, for convenience classed as pre-Cambrian, occur

as several unconformable groups, chiefly developed in the south where alone

their stratigraphy has been determined. They are unfossiliferous, and in

the absence of undoubted Cambrian, Ordovician and Silurian strata in Africa

they may be regarded as of older date than any of these formations. The

general occurrence of jasper-bearing rocks is of interest, as these are

always present in the ancient pressure-altered sedimentary formations of

America and Europe. Some unfossiliferous conglomerates, sandstones and

dolomites in South Africa and on the west coast are considered to belong to

the Cambrian, Ordovician and Silurian formations, but merely from their

occurrence beneath strata yielding Devonian fossils. In Cape Colony the

Silurian age of the Table Mountain Sandstone is based on such evidence.

The Devonian and Carboniferous formations are well represented in the

north and south and in northern Angola.

Up to the close of the palaeozoic period the relative positions of the

ancient land masses and oceans remain unsolved; but the absence of marine

strata of early palaeozoic age from Central Africa points to there being

land in this direction. In late Carboniferous times Africa and India were

undoubtedly united to form a large continent, called by Suess Gondwana

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