Springs—Basins of the Ocean—Origin, Course, and Heads of Rivers—
Hydraulic Systems of Europe—African Rivers—the Nile, Niger, &c.
THE vapour which rises invisibly from the land and water ascends in the
atmosphere till it is condensed by the cold into clouds, which restore
it again to the earth in the form of rain, hail, and snow; hence, there
is probably not a drop of water on the globe that has not been borne on
the wings of the wind. Part of this moisture restored to the earth is
reabsorbed by the air, part supplies the wants of animal and vegetable
life, a portion is carried off by the streams, and the remaining part
penetrates through porous soils till it arrives at a stratum impervious
to water, where it accumulates in subterranean lakes often of great
extent. The mountains receive the greatest portion of the aërial
moisture, and, from the many alternations of permeable and impermeable
strata they contain, a complete system of reservoirs is formed in them,
which, continually overflowing, form perennial springs at different
elevations, which unite and run down their sides in incipient rivers. A
great portion of the water at these high levels penetrates the earth
till it comes to an impermeable stratum below the plains, where it
collects in a sheet, and is forced by hydraulic pressure to rise in
springs, through cracks in the ground, to the surface. In this manner
the water which falls on hills and mountains is carried through
highly-inclined strata to great depths, and even below the bed of the
ocean, in many parts of which there are springs of fresh water. In
boring Artesian wells the water often rushes up with such impetuosity by
the hydrostatic pressure as to form jets 40 or 50 feet high. In this
operation several successive reservoirs have been met with; at St. Ouen,
near Paris, five sheets of water were found; the water in the first four
not being good, the operation was continued to a greater depth; it
consists merely in boring a hole of small diameter, and lining it with a
tube. It rarely happens that water may not be procured in this way; and
as the substratum in many parts of deserts is an argillaceous marl, it
is probable that Artesian wells might be bored with success.
A spring will be intermittent when it issues from an opening in the side
of a reservoir fed from above, if the supply be not equal to the waste,
for the water will sink below the opening, and the spring will stop till
the reservoir is replenished. Few springs give the same quantity of
water at all times; they also vary much in the quantity of foreign
matter they contain. Mountain-springs are generally very pure, the
carbonic acid gas almost always found in them escapes into the
atmosphere, and their earthy matter is deposited as they run along, so
that river-water from such source is soft, while wells and springs in
the plains are hard, and more or less mineral.
The water of springs takes its temperature from that of the strata
through which it passes: mountain-springs are cold, but, if the water
has penetrated deep into the earth, it acquires a temperature depending
on that circumstance.
The temperature of the surface of the earth varies with the seasons to a
certain depth, where it becomes permanent and equal to the mean annual
temperature of the air above. It is evident that the depth at which this
stratum of invariable temperature lies must vary with the latitude. At
the equator the effect of the seasons is imperceptible at the depth of a
foot below the surface: between the parallels of 40° and 52° the
temperature of the ground in Europe is constant at the depth of from 55
to 60 feet: and in the high Arctic regions the soil is perpetually
frozen a foot below the surface. Now, in every part of the world where
experiments have been made, the temperature of the earth increases with
the depth below the constant stratum at the rate of 1° of Fahrenheit for
every 50 or 60 feet of perpendicular depth; hence, should the increase
continue to follow the same ratio, even granite must be in fusion at
little more than five miles below the surface. In Siberia, the stratum
of frozen earth is some hundred feet thick, but below that the increase
of heat with the depth is three times as rapid as in Europe. The
temperature of springs must therefore depend on the depth to which the
water has penetrated before it has been forced to the surface, either by
the hydraulic pressure of water at higher levels, or by steam. If it
never goes below the stratum of invariable temperature, the heat of the
spring will vary with the seasons, more or less, according to the depth
below the surface: should the water come from the constant stratum
itself, its temperature will be invariable; and if from below it, the
heat will be in proportion to the depth to which it has penetrated.
Thus, there may be hot and even boiling springs hundreds of miles
distant from volcanic action and volcanic strata, of which there are
many examples, though they are more frequent in volcanic countries and
those subject to earthquakes. The temperature of hot springs is very
constant, and that of boiling springs has remained unchanged for ages;
shocks of earthquakes sometimes affect the temperature, and have even
stopped them altogether. Jets of steam of high tension are frequent in
volcanic countries, as in Iceland.
Both hot and cold water dissolves and combines with many of the mineral
substances it meets with in the earth, and comes to the surface from
great depths as medicinal springs, containing various ingredients. So
numerous are they that in the Austrian dominions alone there are 1500;
and few countries of any extent are destitute of them. They contain
hydro-sulphuric and carbonic acids, sulphur, iron, magnesia, and other
substances. Boiling springs deposit silex, as in Iceland and in the
Azores; and others of lower temperature deposit carbonate of lime in
great quantities all over the world. Springs of pure brine are rare;
those in Cheshire are rich in salt, and have flowed unchanged 1000
years, a proof of the tranquil state of that part of the globe. Many
substances that lie beyond our reach are brought to the surface by
springs, as naphtha, petroleum, and boracic acid: petroleum is
particularly abundant in Persia, and numberless springs and lakes of it
surround some parts of the Caspian Sea. It is found in immense
quantities in various parts of the world.
RIVERS.
Rivers have had a greater influence on the location and fortunes of the
human race than almost any other physical cause, and, since their
velocity has been overcome by steam navigation, they have become the
highway of the nations.
They frequently rise in lakes, which they unite with the sea; in other
instances they spring from small elevations in the plains, from
perennial sources in the mountains, alpine lakes, melted snow and
glaciers; but the everlasting storehouses of the mightiest floods are
the ice-clad mountains of table-lands.
Rivers are constantly increased, in descending the mountains and
traversing the plains, by tributaries, till at last they flow into the
ocean, their ultimate destination and remote origin. “All rivers run
into the sea, yet the sea is not full,” because it gives in evaporation
an equivalent for what it receives.
The Atlantic, the Arctic, and the Pacific Oceans are directly or
indirectly the recipients of all the rivers, therefore their basins are
bounded by the principal watersheds of the continents; for the basin of
a sea or ocean does not mean only the bed actually occupied by the
water, but comprehends also all the land drained by the rivers which
fall into it, and is bounded by an imaginary line passing through all
their sources. These lines generally run through the elevated parts of a
country that divide the streams which flow in one direction from those
that flow in another. But the watershed does not coincide, in all cases,
with mountain-crests of great elevation, as the mere convexity of a
plain is often sufficient to throw the streams into different
directions.
From the peculiar structure of the high land and mountain-chains, by far
the greater number of important rivers on the globe flow into the ocean
in an easterly direction, those which flow to the south and north being
the next in size, while those that flow in a westerly direction are
small and unimportant.
The course of all rivers is changed when they pass from one geological
formation to another, or by dislocations of the strata: the sudden
deviations in their directions are generally owing to these
circumstances.
None of the European rivers flowing directly into the Atlantic exceed
the fourth or fifth magnitude, except the Rhine; the rest of the
principal streams come to it indirectly through the Baltic, the Black
Sea, and the Mediterranean. It nevertheless receives nearly half the
waters of the old continent, and almost all the new, because the Andes
and Rocky Mountains, which form the watershed of the American continent,
lie along its western side, and the rivers which rise on the western
slope of the Alleghanies are tributaries to the Mississippi, which comes
indirectly into the Atlantic by the Gulf of Mexico.
The Arctic Ocean drains the high northern latitudes of America, and
receives those magnificent Siberian rivers that originate in the Altaï
range from the Steppe of the Kerghis to the extremity of Kamtchatka, as
well as the very inferior streams of North European Russia. The running
waters of the rest of the world flow into the Pacific. The Caspian and
Lake Aral are mere salt-water lakes, which receive rivers but emit none.
However, nearly one-half of all the running water in Europe falls into
the Black Sea and the Caspian.
Mountain-torrents gradually lose velocity in their descent to the low
lands by friction, and when they enter the plains their course becomes
still more gentle, and their depths greater. A slope of one foot in 200
prevents a river from being navigable, and a greater inclination forms a
rapid or cataract. The speed, however, does not depend entirely upon the
slope, but also upon the height of the source of the river, and the
pressure of the body of water in the upper part of its course;
consequently, under the same circumstances, large rivers run faster than
small, but in each individual stream the velocity is perpetually varying
with the form of the banks, the winding of the course, and the changes
in the width of the channel. The Rhone, one of the most rapid European
rivers, has a declivity of one foot in 2620, and flows at the rate of
120 feet in a minute; the sluggish rivers in Flanders have only one-half
that velocity. The Danube, the Tigris, and the Indus are among the most
rapid of the large rivers. In flat countries rivers are generally more
meandering, and thus they afford a greater amount of irrigation; the
windings of the Vistula are nearly equal to nine-tenths of its direct
course from its source to its mouth.
When one river falls into another, the depth and velocity are increased,
but not always proportionally to the width of the channel, which
sometimes even becomes less, as at the junction of the Ohio with the
Mississippi. When the angle of junction is very obtuse, and the velocity
of the tributary stream great, it sometimes forces the water of its
primary to recede a short distance. The Arve, swollen by a freshet,
occasionally drives the water of the Rhone back into the Lake of Geneva;
and it once happened that the force was so great as to make the
mill-wheels revolve in a contrary direction.
Streams sometimes suddenly vanish, and after flowing underground to some
distance reappear at the surface, as in Derbyshire. Instances have
occurred of rivers suddenly stopping in their course for some hours, and
leaving their channels dry. On the 26th of November, 1838, the water
failed so completely in the Clyde, Nith, and Teviot, that the mills were
stopped eight hours in the lower part of their streams. The cause was
the coincidence of a gale of wind and a strong frost, which congealed
the water near their sources. Exactly the contrary happens in the
Siberian rivers, which flow from south to north over so many hundreds of
miles; the upper parts are thawed, while the lower are still frozen, and
the water, not finding an outlet, inundates the country.
The alluvial soil carried down by streams is gradually deposited as
their velocity diminishes; and if they are subject to inundations, and
the coast flat, it forms deltas at their mouths; there they generally
divide into branches, which often join again, or are united by
transverse channels, so that a labyrinth of streams and islands is
formed. Deltas are sometimes found in the interior of the continents at
the junction of rivers, exactly similar to those on the ocean, though
less extensive: deltas are said to be maritime, lacustrine, or
fluviatile, according as the stream that forms them falls into the sea,
a lake, or another river.
Tides flow up rivers to a great distance, and to a height far above the
level of the sea: the tide is perceptible in the river of the Amazons
576 miles from its mouth, and it ascends 255 miles in the Orinoco.
In the temperate zones rivers are subject to floods from autumnal rains,
and the melting of the snow, especially on mountain-ranges. The Po, for
example, spreads desolation far and wide over the plains of Lombardy;
but these torrents are as variable in their recurrence and extent as the
climate which produces them. The inundations of the rivers in the torrid
zone, on the contrary, occur with a regularity peculiar to a region in
which meteoric phenomena are uniform in all their changes. These floods
are due to the periodical rains, which, in tropical countries, follow
the cessation of the trade-winds after the vernal equinox and at the
turn of the monsoons, and are thus dependent on the declination of the
sun, the immediate cause of all these variations. The melting of the
snow no doubt adds greatly to the floods of the tropical rivers which
rise in high mountain-chains, but it is only an accessory circumstance;
for although the snow-water from the Himalaya swells the streams
considerably before the rains begin, yet the principal effect is owing
to the latter, as the southern face of the Himalaya is not beyond the
influence of the monsoon, and the consequent periodical rains, which
besides prevail all over the plains of India traversed by the great
rivers and their tributaries.
Under like circumstances, the floods of rivers, whose sources have the
same latitude, take place at the same season; but the periods of the
inundations of rivers on one side of the equator are exactly the
contrary of what they are in rivers on the other side of it, on account
of the declination of the sun. The flood in the Orinoco is at its
greatest height in the month of August, while that of the river of the
Amazons, south of the equinoctial line, is at its greatest elevation in
March.[117] The commencement and end of the annual inundations in each
river depend upon the mean time of the beginning, and on the duration of
the rains in the latitudes traversed by its affluents. The periods of
the floods in such rivers as run towards the equator are different from
those flowing in an opposite direction; and as the rise requires time to
travel, it happens at regular but different periods in various parts of
the same river, if very long. The height to which the water rises in the
annual floods depends upon the nature of the country, but it is
wonderfully constant in each individual river where the course is long;
for the inequality in the quantity of rain in a district drained by any
of its affluents is imperceptible in the general flood, and thus the
quantity of water carried down is a measure of the mean humidity of the
whole country comprised in its basin from year to year. By the admirable
arrangement of these periodical inundations the fresh soil of the
mountains, borne down by the water, enriches countries far remote from
their source. The waters from the high lands designated as the Mountains
of the Moon, and of Abyssinia, have fertilized the banks of the Nile
through a distance of 2500 miles for thousands of years.
When rivers rise in mountains, water communication between them in the
upper parts of their course is impossible; but when they descend to the
plains, or rise in the low lands, the boundaries between the countries
drained by them become low, and the different systems may be united by
canals. It sometimes happens in extensive and very level plains, that
the tributaries of the principal streams either unite or are connected
by a natural canal, by which a communication is formed between the two
basins—a circumstance advantageous to the navigation and commerce of
both, especially where the junction takes place far inland, as on the
Orinoco and Amazons in the interior of South America. The Rio Negro, one
of the largest affluents of the latter, is united to the Upper Orinoco
in the plains of Esmeralda by the Cassiquiare—a stream as large as the
Rhine, with a velocity of 12 feet in a second. Baron Humboldt observes
that the Orinoco, sending a branch to the Amazons, is, with regard to
distance, as if the Rhine should send one to the Seine or Loire. At some
future period this junction will be of great importance. These
bifurcations are frequent in the deltas of rivers, but very rare in the
interior of continents. The Mahamuddy and Godavery, in Hindostan, seem
to have something of the kind; and there are several instances in the
great rivers of the Indo-Chinese peninsula.
The hydraulic system of Europe is eminently favourable to inland
navigation, small as the rivers are in comparison with those in other
parts of the world; but the flatness of the great plain, and the lowness
of its watershed, are very favourable to the construction of canals. In
the west, however, the Alps and German mountains divide the waters that
flow to the Atlantic on one side, and to the Mediterranean and Black Sea
on the other; but in the eastern parts of Europe the division of the
waters is merely a more elevated ridge of the plain itself, for in all
plains such undulations exist, though often imperceptible to the eye.
This watershed begins on the northern declivity of the Carpathian
Mountains, about the 23d meridian, in a low range of hills running
between the sources of the Dnieper and the tributaries of the Vistula,
from whence it winds in a tortuous course along the plain to the Valdai
table-land, which is its highest point, 1200 feet above the sea; it then
declines northward towards Onega, about the 60th parallel, and lastly
turns in a very serpentine line to the sources of the Kama in the Ural
mountains near the 62d degree of north latitude. The waters north of
this line run into the Baltic and White Sea, and, on the south of it,
into the Black Sea and the Caspian.
Thus, Europe is divided into two principal hydraulic systems; but since
the basin of a river comprehends all the plains and valleys drained by
it and its tributaries from its source to the sea, each country is
subdivided into as many natural divisions or basins as it has primary
rivers, and these generally comprise all the rich and habitable parts of
the earth, and are the principal centres of civilization, or are capable
of becoming so.
The streams to the north of the general watershed are very numerous;
those to the south are of greater magnitude. The systems of the Volga
and Danube are the most extensive in Europe; the former has a basin
comprising 640,000 square miles, and is navigable throughout the greater
part of its course of 1900 miles. It rises in a small lake on the slopes
of the Valdai table-land, 550 feet above the level of the ocean, and
falls into the Caspian, which is 83 feet 7 inches below the level of the
Black Sea, so that it has a fall of 633 feet in a course of more than
2400 miles. It carries to the Caspian one-seventh of all the river-water
of Europe.
Danube drains 300,000 square miles, and receives 60 navigable
tributaries. Its quantity of water is nearly as much as that of all the
rivers that empty themselves into the Black Sea taken together. Its
direct course is 900 miles, its meandering line is 2400. It rises in the
Black Forest at an elevation of 2850 feet above the level of the sea, so
that it has considerable velocity, which, as well as rocks and rapids,
impedes its navigation in many places, but it is navigable downwards,
through Austria, for 600 miles, to New Orsova, from whence it flows in a
gentle current to the Black Sea. The commercial importance of these two
rivers is much increased by their flowing into inland seas. By canals
between the Volga and the rivers north of the watershed, the Baltic and
White Seas are connected with the Black Sea and the Caspian; and the
Baltic and Black Sea are also connected by a canal between the Don and
the Dnieper. Altogether, the water system of Russia is the most
extensive in Europe.
The whole of Holland is a collection of deltoid islands, formed by the
Rhine, the Meuse, and the Scheldt—a structure very favourable to
commerce, and which has facilitated an extensive internal navigation.
The Mediterranean is already connected with the North Sea by the canal
which runs from the Rhone to the Rhine; and this noble system, extended
over the whole of France by 7591 miles of inland navigation, has
conduced mainly to the improved state of that great country.
Many navigable streams rise in the Spanish mountains; of these the Tagus
has depth enough for the largest ships as high as Lisbon. Its actual
course is 480 miles, but its direct line much less. In point of
magnitude, however, the Spanish rivers are of inferior order, but canals
have rendered them beneficial to the country. Italy is less favoured in
her rivers, which only admit vessels of small burthen; those on the
north are by much the most important, especially the Po and its
tributaries, which by canals connect Venice and Milan with various
fertile provinces of Northern Italy but whatever advantages nature has
afforded to the Italian states have been improved by able engineers,
both in ancient and modern times.
The application of the science of hydraulics to rivers took its rise in
Northern Italy, which has been carried to such perfection in some
points, that China is the only country which can vie with it in the
practice of irrigation. The lock on canals was in use in Lombardy as
early as the 13th century, and in the end of the 15th it was applied to
two canals which unite the Ticino to the Adda, by that great artist and
philosopher Leonardo da Vinci: about the same time he introduced the use
of the lock into France.[118]
Various circumstances combine to make the British rivers more useful
than many others of greater magnitude. The larger streams are not
encumbered with rocks or rapids; they all run into branches of the
Atlantic; the tides flow up their channels to a considerable distance;
and above all, though short in their course, they end in wide estuaries
and sounds, capable of containing whole navies—a circumstance that gives
an importance to streams otherwise insignificant, when compared with the
great rivers of either the old or new continent.
The Thames, whose basin is only 5027 square miles, and whose length is
but 240 miles, of which, however, 204 are navigable, spreads its
influence over the remotest parts of the earth; its depth is sufficient
to admit large vessels even up to London, and throughout its navigable
course a continued forest of masts display the flags of every nation:
its banks, which are in a state of perfect cultivation, are the seat of
the highest civilization, moral and political. Local circumstances have
undoubtedly been favourable to this superior development, but the
earnest and energetic temperament of the Saxon races has rendered the
advantages of their position available. The same may be said of other
rivers in the British islands, where commercial enterprise and activity
vie with that on the Thames. There are 2790 miles of canal in Britain,
and, including rivers, 5430 miles of inland navigation, which, in
comparison with the size of the country, is very great; it is even said
that no part of England is more than 15 miles distant from water
communication.
On the whole, Europe is fortunate with regard to its water systems, and
its inhabitants are for the most part alive to the bounties which
Providence has bestowed.
AFRICAN RIVERS.
In Africa the tropical climate and the extremes of aridity and moisture
give a totally different character to its rivers. The most southerly
part is comparatively destitute of them, and those that do exist are of
inferior size, except the Gariep, or Orange River, which has a long
course on the table-land, but is nowhere navigable. From the eastern
edge of the table-land of South Africa, which is very abrupt, rise all
those rivers which flow across the plains of Mozambique and Zanguebar to
the Indian Ocean. Of these, the Zambesi, or Quillimane, is probably the
largest: it is said to have a course of 900 miles, and to be navigable
during the rains for 200 or 300 miles from its mouth. The Ozay, not far
south of the equator, is also believed to be of great extent, and the
Juba, more to the north; all these streams have little water at their
mouths during the dry season, but in the rainy season they are
navigable. Some of those still farther north do not reach the sea at all
times of the year, but end in lakes and marshes, as the Haines and
Hawash. The first, after coming to within a small distance of the Indian
Ocean, runs southward parallel to the coast, and falls into a very large
and deep lake about a degree north of the equator. Between the Hawash
and the Straits of Bab-el-Mandeb there is no river of any note. In many
parts of the coast, near the rivers, grain ripens all the year, yielding
from 80 to 150 fold, and every eastern vegetable production might be
raised. The Hawash runs through a low desert country inhabited by the
Dankali Beduins: that river is the recipient of the waters which come
from the eastern declivity of the table-land of Abyssinia, while the
Nile receives those of the counter slope.
The part of the table-land between the 18th parallel of south latitude
and the equator is the origin from whence the waters flow to the
Atlantic on one hand, and to the Mediterranean on the other. Those which
go to the Atlantic rise south of Lake N’yassi, chiefly in a ridge of no
great elevation which runs from S.W. to N.E. to the west of the
dominions of the Cambeze, and, after falling in cascades and rapids
through the chains that border the table-land on the west, fertilize the
luxuriant maritime plains of Benguela, Congo, Angola, and Loando. The
Zaire, or Congo, by much the largest of these, is navigable for 140
miles, where the ascent of the tide is stopped by cataracts. The lower
course of this river is 5 or 6 miles broad, full of islands, and 160
fathoms deep at its mouth. Its upper course, like that of most of these
rivers, is unknown; the greater number are fordable on the table-land,
but, from the abrupt descent of the high country to the maritime plains,
none of them afford access to the interior of South Africa.
The mountainous edge of the table-land, with its terminal projections,
Senegambia and Abyssinia, which separate the northern from the southern
deserts, are the principal source of running water in Africa. Various
rivers have their origin in these mountainous regions, of which the Nile
and the Niger yield in size only to some of the great Asiatic and
American rivers. In importance and historical interest the Nile is
inferior to none.
Two large rivers unite their streams to form the Nile—the Bahr-el-Abiad,
or White Nile, and the Bahr-el-Azrek, or Blue Nile; but the latter is so
far inferior to the Bahr-el-Abiad that it may almost be regarded as a
tributary. The main stream has never been ascended by any traveller
above 4° 42ʹ 42ʺ north latitude, where a ledge of gneiss crossing it
arrested the progress of the second expedition sent by the Viceroy of
Egypt to discover its source. Bahr-el-Abiad, or the true Nile, is
supposed, from the report of the natives, to rise, under the name of the
Tubiri, at a comparatively small distance from the sea, in the country
of Mono Moézi, which is a continuation of the high plateau of Abyssinia,
situate to the north of the great Lake Zambéze, or N’yassi. The natives
say that it flows from the lake itself; at all events it seems to be
pretty certain that its origin is in the mountainous or hilly country of
Mono Moézi, a word which in all the languages of that part of Africa
signifies the Moon: hence, the Nile has been said, since the days of
Ptolemy, to rise in the Mountains of the Moon. Amidst many windings it
takes a general direction towards the N.E. to the 14th northern
parallel, whence it follows the same course till its junction near
Khartum with the Blue Nile in the plains of Sennaar.
The Shoaberri and Godjeb, the chief affluents of the White Nile, come
from the east; the former makes a great circuit round the country of
Berri before it falls into the Nile, and the Godjeb, which has its
origin in the great forest already mentioned, in the Galla country,
south of Abyssinia, makes a similar spiral détour round Kaffa, and under
the name of Subat joins the Nile, which it enlarges to nearly double its
size.
The Abyssinian branch of the Nile, known as the Bahr-el-Azrek, or Blue
River, rises under the name of the Dedhesa in the Galla country, south
of Abyssinia, about 73 miles west of Sokka, the capital of Enarea. It
springs from a swampy meadow in the same elevated plains where the
Godjeb and other affluents of the White Nile originate, and after a
completely spiral course, in which it separates the kingdoms of Guma and
Enarea, it maintains a general north-westerly direction till it joins
the White Nile at Khartum. Of the many tributaries to the Blue River,
the Abái, the Nile of Bruce, is the greatest and most celebrated. Its
sources are in a swampy meadow near Mount Giesk, in the district of
Sákkata, from whence it takes a circular direction round the peninsula
of Gojam, passing through Lake Dembea, and receiving many affluents from
the mountain-chain that forms the cone of the peninsula, and at last
falls into the Dedhesa or Bahr-el-Azrek, in about 11° N. latitude. From
that point no stream of any consequence joins either the Blue River, or
the united streams of the Blue and White Rivers, till 160 miles below
their confluence, where the Atbarah, or Takkazie, falls into it. This
river, which is the principal tributary of the Nile, is formed by two
branches. The Takkazie rises in the mountains of Lasta, near Lalíbata,
one of the most celebrated places in Abyssinia, remarkable for its
churches hewn out of the living rock, and the Tselari, which springs
from Mount Biála, the northern extremity of the high land of Lasta,
which divides the head waters of the two branches. The united stream,
after winding like the other rivers of this country, joins the Nile in
18° N. latitude, the northern limit of the tropical rains.
The Abyssinian rivers in the early part of their course are little more
than muddy brooks in the dry season, but during the rains they inundate
the plains. They break from the table-lands through fissures in the
rocky surface, which are at first only a few yards wide, but gradually
increase to several miles; the streams form cataracts from 80 to more
than 100 feet high, and then continue to descend by a succession of
falls and rapids, which decrease in height as they go northwards to join
the main stream. The Takkazie takes its name of “The Terrible” from the
impetuosity with which it rushes through the chasms and over the
precipices of the mountains.
A peculiarity of most of the principal affluents of the Nile is their
spiral course, so that, after having formed a curve of greater or less
extent, generally round insulated mountain masses, they return upon
themselves at a short distance from their sources. It is by no means
improbable that the head stream of the Nile itself takes a spiral course
round a lofty mountain mass, similar to the snow-clad mountains of
Sámien and Káffa.[119]
From the Takkazie down to the Mediterranean, a distance of 1200 miles,
the Nile does not receive a single brook. The first part of that course
is interrupted by cataracts, from the geological structure of the Nubian
desert, which consists of a succession of broad sterile terraces,
separated by ranges of rocks running east and west. Over these the Nile
falls in nine or ten cataracts, the last of which is at Es-Souan
(Syene), where it enters Egypt. Most of them are only rapids, where each
successive fall of water is not a foot high. That they were higher at a
former period has recently been ascertained by Dr. Lepsius, the very
intelligent traveller sent by the King of Prussia at the head of a
mission to explore that country. He found a series of inscriptions on
the rocks at Sennaar, marking the height of the Nile at different
periods; and it appears from these, that in that country the bed of the
river had been 30 feet higher than it is now.
Fifteen miles below Cairo, and at 90 miles from the sea, the Nile is
divided into two branches, of which one, running in a northerly
direction, enters the Mediterranean below Rosetta; the other, cutting
Lower Egypt into two nearly equal parts, enters the sea above Damietta,
so that the delta between these two places has a sea-coast of 187 miles.
The fall from the great cataract to the sea is two inches in a mile.
The basin of the Nile, occupying an area of 500,000 square miles, has an
uncommon form: it is wide in Ethiopia and Nubia, but for the greater
part of a winding course of 2750 miles it is merely a verdant line of
the softest beauty, suddenly and strongly contrasted with the dreary
waste of the Red Desert. Extending from the equatorial far into the
temperate zone, its aspect is less varied than might have been expected
on account of the parched and showerless country it passes through.
Nevertheless, from the great elevation of the origin of the river, the
upper part has a perpetual spring, though within a few degrees of the
equator. At the foot of the table-land of Abyssinia the country is
covered with dense tropical jungles, while the rest of the valley is
rich soil, the detritus of the mountains for thousands of years.
As the mean velocity of the Nile, when not in flood, is about two miles
and a half an hour, a particle of water would take twenty-two days and a
half to descend from the junction of the Takkazie to the sea; hence, the
retardation of the annual inundations of the Nile in its course is a
peculiarity of this river, owing to some unknown cause towards its
origin which affects the whole stream. In Abyssinia and Sennaar the
river begins to swell in April, yet the flood is not sensible at Cairo
till towards the summer solstice; it then continues to rise about a
hundred days, and remains at its greatest height till the middle of
October, when it begins to subside, and arrives at its lowest point in
April and May. The height of the flood in Upper Egypt varies from 30 to
35 feet; at Cairo it is 23, and in the northern part of the delta only 4
feet.
Anubis, or Sirius, the Dog-star, was worshipped by the Egyptians, from
its supposed influence on the rising of the Nile. According to
Champollion, their calendar commenced when the heliacal rising of that
star coincided with the summer solstice—the time at which the Nile began
to swell at Cairo. Now this coincidence made the nearest approach to
accuracy 3291 years before the Christian era; and as the rising of the
river still takes place precisely at the same time and in the same
manner, it follows that the heat and periodical rains in Upper Ethiopia
have not varied for 5000 years. In the time of Hipparchus, the summer
solstice was in the sign of Leo, and probably about that period the
flowing of the fountains from the mouths of lions of basalt and granite
was adopted as emblematical of the pouring forth of the floods of the
Nile. The emblem is still common in Rome, though its origin is probably
forgotten, and the signs of the Zodiac have moved backwards more than
30°.
The two greatest African rivers, the Nile and the Niger, are dissimilar
in almost every circumstance; the Nile, discharging for ages into a sea,
the centre of commerce and civilization, has been renowned by the
earliest historians, sacred and profane, for the exuberant fertility of
its banks, and for the learning and wisdom of their inhabitants, who
have left magnificent and imperishable monuments of their genius and
power. Egypt was for ages the seat of science, and by the Red Sea it had
intercourse with the most highly cultivated nations of the east from
time immemorial. The Niger, on the contrary, though its rival in
magnitude, and running through a country glowing with all the brilliancy
of tropical vegetation, has ever been inhabited by barbarous or
semi-barbarous nations; and its course till lately was little known, as
its source still is. In early ages, before the Pillars of Hercules had
been passed, and indeed long afterwards, the Atlantic coast of Africa
was an unknown region, and thus the flowing of the Niger into that
lonely ocean kept the natives in their original rude state. Such are the
effects of local circumstances on the intellectual advancement of man.
The sources of the Niger, Joliba, or Quorra, are supposed to be on the
northern side of the Kong Mountains, in the country of Bambarra, more
than 1600 feet above the level of the sea. From thence it runs north,
and, after passing through Lake Debo, makes a wide circuit in the plains
of Soudan to Timbuctoo through eight or nine degrees of latitude: then
bending round, it again approaches the Kong Mountains, at the distance
1000 miles in a straight line from its source; and having threaded them,
it flows across the low lands into the Gulf of Guinea, a course of 2300
miles. In the plains of Soudan it receives many very large affluents
from the high land of Senegambia on the west, and the Tchadda on the
east—a navigable river larger than itself, probably the outlet of the
great lake Tchad, which drains the high land of Komri, designated by the
ancients as the Mountains of the Moon, and falls into it a little below
Fundah, after a course of some hundred miles: thus, the Niger probably
affords an uninterrupted water-communication from the Atlantic to the
heart of Africa.[120] Long before leaving the plains of Soudan it
becomes a noble river with a smooth stream, gliding at the rate of from
5 to 8 miles an hour, varying in breadth from 1 to 8 miles. Its banks
are studded with densely populous towns and villages, groves of
palm-trees, and cultivated fields.
This great river divides into three branches near the head of a delta
which is equal in area to Ireland, intersected by navigable branches of
the principal stream in every direction. The soil is rich mould, and the
vegetation so rank that the trees seem to grow out of the water. The
Nun, which is the principal or central branch, flows into the sea near
Cape Formosa, and is that which the brothers Lander descended. There
are, however, six rivers which run into the Bight of Benin, all
communicating with the Niger, and with one another. The old Calabar is
the most eastern; it rises in the high land of Calbongos, and is united
to the Niger by a natural canal. The Niger, throughout its long winding
course, lies entirely within the tropic of Cancer, and is consequently
subject to periodical inundations, which reach their greatest height in
August, about 40 or 50 days after the summer solstice. The plains of
Soudan are then covered with water and crowded by boats. These fertile
regions are inaccessible to Europeans from the pernicious climate, and
dangerous from the savage condition of many of the tribes.
The coast of Guinea, west from the Niger, is watered by many streams, of
no great magnitude, from the Kong Mountains. The table-land of
Senegambia is the origin of the Rio Grande, the Gambia, the Senegal, and
others of great size; and also of many of an inferior order that
fertilize the luxuriant maritime plains on the Atlantic. Their navigable
course is cut short by a semicircular chain of mountains which forms the
boundary of the high land, through which they thread their way in rapids
and cataracts. The Gambia rises in Foula Toro, and after a course of
about 600 miles enters the Atlantic by many branches connected by
natural channels, supposed at one time to be separate rivers. The
Senegal, the largest river in this part of Africa, is 850 miles long. It
receives many tributaries in the upper part of its course, and the lower
is full of islands. It drains two lakes, has several tributaries, and is
united to the basin of the Gambia by the river Neriko.