Africa

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

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