Учебный материал
РОССИЙСКОЙ КОЛЛЕКЦИИ РЕФЕРАТОВ (с) 1996
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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