252 AFRICA [PHYSICAL of a mesozoic age. The surface of the South African continent has not been diversified in recent times by the outpouring of lava streams, or broken up by the efforts of subterranean heat to escape. Nor lias it been sub jected to those great oscillations by which the surfaces of many other countries have been so placed under the waters of the ocean as to have been strewed over with erratic blocks and marine exuviax The interior of South Africa may therefore be viewed as a country of very ancient conservative terrestrial character. Knowledge of the special geology of Africa is yet confined to the few parts of the continent in which Europeans have perma nently settled. In this respect the southern region of the Cape Colony and Natal have advanced furthest, and their geological features have been mapped out with some accuracy. Elsewhere in the continent, excepting in Algeria and Angola, light has only been thrown along the line followed by the few explorers who have given attention to this subject. Among the minerals of Africa, salt is widely distributed, though in some districts wholly wanting. Thus in the Abyssinian high laud the salt, which is brought up in small blocks from the depressed salt plain on the Red Sea coast beneath, is so valued as to be used as a money currency ; and in the native kingdoms of South Central Africa, the salt districts are royal possessions strictly guarded. Metals seem nowhere very abundant. Gold is perhaps the most generally distributed. The gold-fields of the Transvaal Republic and of the country which extends thence to the Zambeze, are numerous; but no yield has as yet been dis covered of sufficient quantity to overcome the difficulties of working, and of transport to the distant sea-ports, to which no navigable rivers lead from this region. Copper is known to exist in large quantities in the mountains of native kingdoms of the centre of South Africa ; and one of the objects of Dr Livingstone s present journey is to visit the famed copper country of Katanga south-west of the Tanganyika Lake. The diamond-fields in the districts of the Vaal and Orange rivers north of the Cape Colony are now steadily worked, and give good returns. Africa is the only one of the continents of the globe which lies equally to north and south of the equator, and the portions of it which extend beyond the tropics do not advance far into the temperate zones. From this it results that Africa, besides being the warmest of all the continents, has also the most equal distribution of the sun s heat during the seasons over the parts which lie north and south of the central line. Winds and rain, depending on the distribution of heat, are also correspondingly developed in these two great divisions of the continent, and the broad landscape zones, passing from humid forest to arid sandy desert, also agree exactly with one another north and south of Equatorial Africa. Between 10 N. and 10 S. of the equator, but especially in that portion of it the outskirts of which have only as yet been reached by travellers, Africa appears to be a land of den. : e tropical forest. Wherever it has been penetrated, travellers speak of an excessively rank vegetation ; passage has to be forced through thick underwood and creeping plants, between giant trees, Avhose foliage shuts out the sun s rays; and the land teems with animal and insect life of every form and colour. Describing the forests of Manyuema country, west of the Tanganyika Lake, Living stone says " Into these [primaeval forests] the sun, though vertical, cannot penetrate, excepting by sending down at midday thin pencils of rays into the gloom. The rain water stands for months in stagnant pools made by the feet of elephants. The climbing plants, from the size of a whipcord to that of a man-of-war s hawser, are so numerous, that the ancient path is the only passage. When one Northerr and southern pastoral belts. of the giant trees falls across the road, it forms a Avail breast high to be climbed over, and the mass of tangled ropes brought down makes cutting a path round it a work of time which travellers never undertake." Here there is a double rainy season, and the rainfall is excessive. To north and south of this central belt, where the rainfall diminishes, and a dry and wet season divides the year, the forests gradually open into a park-like country, and then merge into pastoral grass-lands. In North Africa this pastoral belt is occupied by the native states of the Soudan, from Abyssinia westward, in the parallel of Lake Chad, to the Gambia on the Atlantic coast; and corre sponding to this in the south, are the grass-lands stretching across the continent from the Zambeze to southern Angola and Benguela. The pastoral belts again gradually pass into the dry, almost rainless desert zones of the Sahara in Deserts, the north, and the Kalahari desert in the south, which present many features of similarity. The extremities of the continent, to which moisture is carried from the neighbouring oceans, again pass into a second belt of pastoral or agricultural land, in the north ward slopes of the plateaus of Barbary, Marocco, Algeria, and Tunis, corresponding with the seaward terraces of cultivated land in the Cape Colony in the south. Taking a broad view of the hydrography of Africa, there Rivera are two great areas of continental drainage, one in the north, the other in the south, from which no water escapes directly to the ocean. These correspond almost exactly with the two desert belts of the Sahara and the Kalahari above described. The whole of the remaining portions of the continent, its forests and pastoral districts, in which the greater rainfall gives greater power to the rivers, are drained by streams Avhich find their Avay to the ocean on one side or other, generally forcing a passage through some, natural or Avaterworn gorge in the higher circle of mountains which run round the outer edges of the great plateau. By far the larger portion of the oceanic drainage of the continent is to the Atlantic and its branch the Mediter ranean, to Avhich the Nile, Niger, OgoA r ai, Congo, and Orange rivers fioAv. The great rivers Avhich drain on the opposite side, to the Indian Ocean, are the Juba, Zambeze, and Limpopo ; Avhilst the northern continental basin, by far more extensive than the southern, has only one great riA r er, the Shari, which supplies Lake Chad. It must be noticed that the capabilities of the African riA ers, as highways of approach to the interior of the con tinent, are exceedingly small in comparison Avith those of the other great continents of the globe, most of them being cither barred at their mouths, or by rapids at no great distance from the coast. It is OAving to this physical cause mainly that the African continent has remained for so many centuries a sealed book to the civilised Avorld. On the other hand, it must be observed, that Avhen these outer barriers have been passed, the great interior of the land, in its most productiA T e regions, possesses a netAvork of A-a.st rivers and lakes, unsurpassed in extent by those of any country of the Avorld, by means of Avhich the resources of Central Africa may in future be thoroughly developed. The Nile is the oldest of historical rivers, and afforded the only means of subsistence to the earliest ciA-iliscd people on earth, and yet the origin of this riA r er remained an enigma almost to the present day. Though it drains a larger area than any other river of Africa, upwards of 1,000,000 square miles, and in this respect is one of the largest rivers of the globe, the Nile, passing for a great portion of its loAver course through the desert belt of North Africa, and receiAing no tributaries there, loses much of its volume by CA r aporation, and is far surpassed in the quantity of Avater coiweyed to the ocean by the Congo, in the moist equatorial zone. The great labours of Dr
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