If we look at the map of Africa, we shall find that the great lakes, which form such an important physical feature of the continent, are located chiefly in the southern and eastern sections of it, but are distributed overall the great drainage systems. Let us take a little review of the lake system.
Both lakes of the Nile basin, the Victoria and Albert Nyanza lakes, are really great fresh-water seas.
If the present estimate of this great extent should ultimately prove to be fairly correct, they are the rivals even of the great American lakes in being the greatest expanse of fresh water on the face of the globe.
In 1889, a great lake lying three hundred miles northeast of the Victoria Nyanza was discovered. It has been named Lake Rudolf. It is about one hundred and sixty two miles long and over twenty miles wide.
The princ.i.p.al lakes of the Congo basin are Lake Bangweolo, or Bemba, one hundred and fifty miles long from east to west, and Lake Moero, having a length of sixty miles. There are several lakes of this basin still unvisited. They are said to be of vast extent and to lie two thousand feet above the level of the sea.
Lake Nya.s.sa belongs to the Zambesi basin. It covers an area of nearly nine thousand miles in this great river basin. Lake Shirwa, on the plateau southeast of Lake Nya.s.sa, is enclosed by mountains. It has an elevation of two thousand feet above the sea. Its water is brackish and has no outlet. Lake Tanganyika occupies an area of more than ten thousand square miles. A broad channel unites it with Lake Liemba, in the south. No outlet was for many years discovered for Tanganyika. It is probably a continental lake; for its waters are not perfectly fresh, and its drainage is very small.
Lake Tchad is the greatest lake of the continental system of North Africa. It consists of a shallow lagoon of very variable extent.
Numerous islands dot its surface. Its waters are fresh and clear, and the overflow is carried off by the Bahr-el-Gazal to the northeast. Lake N"gami is in the southern continental system. It corresponds to Lake Tchad of the northern system. It is a shallow, reedy lagoon. Its extent varies according to the seasons. Its surplus water is carried by the Zuga River off to the eastward. Within the areas of continental drainage, salt lakes occur frequently. a.s.sal Lake, in Abyssinia, is the most remarkable of these salt lakes.
CHAPTER XXVIII.
MOUNTAINS OF AFRICA.
No other portion of land on the surface of the globe is so difficult of access as Africa. This is owing to the mountainous character of large portions of its coast line.
"The contrast between the broken European sh.o.r.es and the ma.s.sive African coasts of the Mediterranean was observed by the earliest geographers; the same continuous, unbroken margin extends along all the sixteen thousand miles of its sh.o.r.e line.
"Guarded by its inhospitable sh.o.r.es, large areas of the interior of the continent are as yet altogether unknown. As a whole, the continent may be regarded as a vast plateau, bordered round by maritime ranges, which form the seaward edges of the interior table-lands."
The ranges of the eastern coast have been so little explored that much has yet to be learned of their character. They extend from the highlands of Abyssinia to the extreme southern point of the continent.
The so-called Mountains of the Moon belong to this system. The early explorers erred when they supposed that they stretched across Central Africa from east to west. So great has been the diversity of opinion, that some authors deny the existence of these mountains.
We must consider the interior of Africa as a vast plateau traversed by mountain chains. The only lowland known to lie within the interior is the section about Lake Tchad.
If we look upon the map of Africa, we shall find that the princ.i.p.al mountain systems are known as the Atlas, the reputed Mountains of the Moon, the Snow, Kong, Crystal, Cameroon, and Lupata.
The Atlas Mountains give character to the Barbary States of Morocco and Algeria. The Mountains of the Moon are supposed to run from south to north, parallel to the eastern coast, and to form the southern continuation of the Abyssinian table-land. The Snow Mountains are found in the southern part of the continent, stretching through Cape Colony.
The Kong Mountains, though outlined upon the map, according to the celebrated English geographer, Keith Johnston, of the Royal Geographical Society, do not exist. We shall read his descriptions of mountain systems later on. It is well to take more than one view of any subject.
The Crystal and Cameroon Mountains stretch along the western border, though at some distance from the coast line, while the Lupata Mountains are found in the region of the Zambesi. But let us look more minutely at these mountain systems, as described by Mr. Johnston.
Beginning at the extreme northeastern corner of Africa, the land suddenly rises west of Suez, at the southern end of the ship ca.n.a.l, to a height of twenty-six hundred feet. Following this, an abrupt chain of heights extends along the western sh.o.r.es of the Red Sea, till the high edge of the Abyssinian highland is reached, seven thousand to eight thousand feet above sea level.
Farther to the south, on the margin of the plateau, rise snow-capped Kenia, eighteen thousand feet, and Kilimanjaro, eighteen thousand seven hundred feet, between the Indian Ocean and the Great Lake region.
Still farther south rise the Livingstone Mountains, to the height of eleven thousand feet, walling in Lake Nya.s.sa. Farther south still rise the steep and wall-like Drachenberg Mountains, to face the Indian Ocean and to round to the terraces which form Cape Colony.
"Turning the high Cape of Good Hope to the Atlantic margin, the same terraced ascents from the sea coast to the borders of the interior present themselves, all along the western side of the continent, from Cape Colony to the head of the Bight of Biafra.
"Round the Guinea coast, beyond the low delta of the Niger, as far as Cape Verd, the plateau edge approaches the coast only at intervals, but the supposed Kong Mountains do not exist.
"In Morocco, the bordering maritime heights are taken up again by the Atlas range, and are continued along the Mediterranean by the plateau of Barbary, by the ranges called the Black Mountains of Tripoli, and by the heights of Barca, farther east, out again to the delta of the Nile."
Within this border, or fringe, of maritime heights thus traced, we may consider all southern Africa as a vast plateau having a general elevation of about three thousand feet above the sea.
The most prominent interior ranges which rise from this section of the plateau are those called the Mushinga Mountains. These "seem to have an east and west direction, separating the wide basins of the Congo and Zambesi Rivers, and the mountains to the westward of Lakes Albert and Victoria Nyanza and Tanganyika." The latter "form the western edge of the great plateau of eastern equatorial Africa, the center of which is occupied by Unyamwezi, and slope down towards the broad vale of the central Congo."
If we look at the map, "Northern Africa, between the higher southern plateau and the mountains of Barbary on the Mediterranean coast, appears to be generally lower, or at an average elevation of from one thousand to fifteen hundred feet above the sea, though the plateau formation remains the same.
"The prominent lines of height known within it are those which extend from the Marrah Mountains of Dafur, between the Nile basin and that of Lake Tchad, northwestward through the mountain land of Tibesti, in the center of North Africa, to the series of plateaus occupied by the Tuareg tribes south of the plateau of Barbary.
[Ill.u.s.tration: CROSSING THE DESERT.]
"A remarkable volcanic belt is traced through the Bight of Biafra in the line of the islands of Ann.o.bon, St. Thomas, Princes, and Fernando Po, ten thousand one hundred and ninety feet high, to the high Cameroon Mountains, thirteen thousand seven hundred and sixty feet high, on the coast of the mainland, and thence inland on the same abrupt line to Mounts Alantika and Mendif, midway to Lake Tchad in the interior."
If we could follow the course taken by the early settlers and the missionaries in Africa, we should, in going from the southern coast northward, have to cross three mountain systems and two table lands, before we could reach the great central plateau.
The mountains would present "steep, wall-like faces on the coast side, as if they were raised to prevent all access to the interior; on the other side they descend gradually to the broad, elevated tracts, which retain the name karroos, barren plains, given them by the natives on account of their general appearance and character."
In such a section as Cape Colony, we might expect that the karroos, enclosed by mountains, would become converted into lakes, did we not remember that little rain falls there, and then for only a brief season.
"The karroos appear to have been lakes at some very remote period in the history of the earth"s surface; for much of the soil is impregnated with salt; shallow salt lakes or marshes are numerous, and beds of sea sh.e.l.ls are to be found here and there."
Nature has looked well to the law of cause and effect; for, while the rivers are dry during some portions of the year, after a tempest the waters flow down over the sides of the mountains in torrents. These, in the course of ages, have worn deep cuts, or valley gorges, called kloofs.
The karroos, or elevated tracts, of which we have read, are not like the vast seas of sand of the Sahara. "They consist of shallow beds of rich soil, which want only the fertilizing power of water to render them most productive. The soil of the karroos is clay and sand, resting on blue slate rock. As the streams are dry for three-fourths of the year, the ground becomes during that period as hard as brick. After a few days of rain, gra.s.ses and other plants with bulbous roots, spring up everywhere from the hard soil in which they have been encased, and soon the land is covered with bright flowers and verdant pasturage."
Probably no part of the globe presents a more beautiful appearance than these karroos when carpeted by the hand of nature. The description of the flowers of Cape Colony by the author of "Life on an Ostrich Farm"
gives one a fair idea of their beauty and variety.
CHAPTER XXIX.
SOME PECULIAR FEATURES OF AFRICAN SOIL.
In making some of his early explorations Livingstone pa.s.sed over a country, the firm, compact soil of which was perfectly level. Here he found a little soil covering a limelike tufa deposit. This extended over a tract of several hundred miles. It supported a vegetation of fine, sweet, short gra.s.s, and baobab and other trees.
In several parts of this tract he found large salt pans, as they are termed. One was fifteen miles broad and one hundred miles long.
Although these curious spots seemed perfectly level, yet they have a slight slope to the northeast, towards which the rain water, which sometimes covers them, gently trickles. The salt dissolved in the water has in this way been gradually transferred to one large pan lying to the northeast. On this may be seen a cake of salt and lime an inch and a half thick. Some of these pans have merely a covering of salty lime; others are covered with a thick deposit of sh.e.l.ls.
These sh.e.l.ls are identical with those of the mollusk species of Lake N"gami. There appear to be three varieties, spiral, univalve, and bivalve.
Livingstone found that in every salt pan of the country there is a spring of water on one side. The water of the spring is brackish. In one instance he found two springs, one salter than the other.
He was of the opinion that the supply could not come from beds of rock salt; for, where the natives have removed the salt from the pans, no new deposit has ever formed.
He thought it probable that these salt deposits are the remains of the slightly brackish lakes of antiquity. Large portions of these lakes must, in the course of ages, have evaporated to leave a deposit where the waters have receded.