No geological change having occurred in ages long anterior to man, as shown by Sir R. I. Murchison theoretically so far back as the year 1852, when Central Africa was utterly unknown, it is natural to suppose that the races that exist upon that surface should be unaltered from their origin. That origin may date from a period so distant, that it preceded the Adamite creation. Historic man believes in a Divinity; the tribes of Central Africa know no God. Are they of our Adamite race? The equatorial portion of Africa at the Nile sources has an average altitude above the sea-level of about 4,000 feet; this elevated plateau forms the base of a range of mountains, that I imagine extends, like the vertebrae of an animal, from east to west, shedding a drainage to the north and south. Should this hypothesis be correct, the southern watershed would fill the Tanganika lake: while farther to the west another lake, supplied by the southern drainage, may form the head of the river Congo. On the north a similar system may drain into the Niger and Lake Tchad: thus the Victoria and the Albert lakes, being the two great reservoirs or sources of the Nile, may be the first of a system of African equatorial lakes fed by the northern and southern drainage of the mountain range, and supplying all the principal rivers of Africa from the great equatorial rainfall. The fact of the centre of Africa at the Nile sources being about 4,000 feet above the ocean, independently of high mountains rising from that level, suggests that the drainage of the Equator from the central and elevated portion must find its way to the lower level and reach the sea. Wherever high mountain ranges exist, there must also be depressions; those situated in an equatorial rainfall must receive the drainage from the high lands and become lakes, the overflow of which must form the sources of rivers, precisely as exemplified in the sources of the Nile from the Victoria and the Albert lakes.
The fact that Sir Roderick Murchison, as a geologist, laid down a theory of the existence of a chain of lakes upon an elevated plateau in Central Africa, which theory has been now in great measure confirmed by actual inspection, induces me to quote an extract from his address at the anniversary meeting of the Royal Geographical Society, 23d May, 1864. In that address, he expressed opinions upon the geological structure and the races of Central Africa, which preceded those that I formed when at the Albert lake. It is with intense interest that I have read the following extract since my return to England:—
"In former addresses, I suggested that the interior mass and central portions of Africa constituting a great plateau occupied by lakes and marshes from which the waters escaped by cracks or depressions in the subtending older rocks, had been in that condition during an enormously long period. I have recently been enabled, through the apposite discovery of Dr. Kirk, the companion of Livingstone, not only to fortify my conjecture of 1852, but greatly to extend the inferences concerning the long period of time during which the central parts of Africa have remained in their present condition, save their degradation by ordinary atmospheric agencies. My view, as given to this Society in 1852, was mainly founded on the original and admirable geological researches of Mr. Bain in the colony of the Cape of Good Hope. It was, that, inasmuch as in the secondary or mesozoic age of geologists, the northern interior of that country was occupied by great lakes and marshes, as proved by the fossil reptile discovered by Bain, and named Dicynodon by Owen, such it has remained for countless ages, even up to the present day. The succeeding journeys into the interior, of Livingstone, Thornton and Kirk, Burton and Speke, and Speke and Grant, have all tended to strengthen me in the belief that Southern Africa has not undergone any of those great submarine depressions which have so largely affected Europe, Asia, and America, during the secondary, tertiary, and quasi modern periods.
"The discovery of Dr. Kirk has confirmed my conclusion. On the banks of an affluent of the Zambesi, that gentleman collected certain bones, apparently carried down in watery drifts from inland positions, which remains have been so fossilized as to have all the appearance of antiquity which fossils of a tertiary or older age usually present. One of these is a portion of the vertebral column and sacrum of a buffalo, undistinguishable from that of the Cape buffalo; another is a fragment of a crocodile, and another of a water-tortoise, both undistinguishable from the forms of those animals now living. Together with these, Dr. Kirk found numerous bones of antelopes and other animals, which, though in a fossil condition, all belonged, as he assured me, to species now living in South Africa.
"On the other hand, none of our explorers, including Mr. Bain, who has diligently worked as a geologist, have detected in the interior any limestones containing marine fossil remains, which would have proved that South Africa had, like other regions, been depressed into oceanic conditions, and re-elevated. On the contrary, in addition to old granitic and other igneous rocks, all explorers find only either innumerable undulations of sandstones, schistose, and quartzose rocks, or such tufaceous and ferruginous deposits as would naturally occur in countries long occupied by lakes and exuberant jungles, separated from each other by sandy hills, scarcely any other calcareous rocks being found except tufas formed by the deposition of landsprings. It is true that there are marine tertiary formations on the coasts (around the Cape Colony, near the mouth of the Zambesi opposite Mozambique, and again on the coasts of Mombas opposite Zanzibar), and that these have been raised up into low-coast ranges, followed by rocks of igneous origin. But in penetrating into the true interior, the traveller takes a final leave of all such formations; and in advancing to the heart of the continent, he traverses a vast region which, to all appearance, has ever been under terrestrial and lacustrine conditions only. Judging, indeed, from all the evidences as yet collected, the interior of South Africa has remained in that condition since the period of the secondary rocks of geologists! Yet, whilst none of our countrymen found any evidences of old marine remains, Captain Speke brought from one of the ridges which lay between the coast and the lake Victoria N'yanza a fossil shell, which, though larger in size, is undistinguishable from the Achatina perdix now flourishing in South Africa. Again, whilst Bain found fossil plants in his reptiliferous strata north of the Cape, and Livingstone and Thornton discovered coal in sandstone, with fossil plants, like those of our old coal of Europe and America,—yet both these mesozoic and palaeozoic remains are terrestrial, and are not associated with marine limestones, indicative of those oscillations of the land which are so common in other countries.
"It is further to be observed, that the surface of this vast interior is entirely exempt from the coarse superficial drift that encumbers so many countries, as derived from lofty mountain-chains from which either glaciers or great torrential streams have descended. In this respect, it is also equally unlike those plains of Germany, Poland, and Northern Russia, which were sea-bottoms when floating icebergs melted and dropped the loads of stone which they were transporting from Scandinavia and Lapland.
"In truth, therefore, the inner portion of Southern Africa is, in this respect, as far as I know, geologically unique in the long conservation of ancient terrestrial conditions. This inference is further supported by the concomitant absence, throughout the larger portion of all this vast area, i.e. south of the Equator, of any of those volcanic rocks which are so often associated with oscillations of the terra firma ["Although Kilimandjaro is to a great extent igneous and volcanic, there is nothing to prove it has been in activity during the historic era.">[
"With the exception of the true volcanic hills of the Cameroons recently described by Burton, on the west coast, a little to the north of the Equator, and which possibly may advance southwards towards the Gaboon country, nothing is known of the presence of any similar foci of sub-aerial eruption all round the coasts of Africa south of the Equator. If the elements for the production of them had existed, the coast-line is precisely that on which we should expect to find such volcanic vents, if we judge by the analogy of all volcanic regions where the habitual igneous eruptions are not distant from the sea, or from great internal masses of water. The absence, then, both on the coasts and in the interior, of any eruptive rocks which can have been thrown up under the atmosphere since the period when the tertiary rocks began to be accumulated, is in concurrence with all the physical data as yet got together. These demonstrate that, although the geologist finds here none of those characters of lithological structure and curiously diversified organic remains which enable him to fix the epochs of succession in the crust of the earth in other quarters of the globe, the interior of South Africa is unquestionably a grand type of a region which has preserved its ancient terrestrial conditions during a very long period, unaffected by any changes except those which are dependent on atmospheric and meteoric influences.
"If, then, the lower animals and plants of this vast country have gone on unchanged for a very long period, may we infer that its human inhabitants are of like antiquity? If so, the Negro may claim as old a lineage as the Caucasian or Mongolian races. In the absence of any decisive fact, I forbear, at present, to speculate on this point; but as, amid the fossil specimens procured by Livingstone and Kirk, there are fragments of pottery made by human hands, we must wait until some zealous explorer of Southern Africa shall distinctly bring forward proofs that the manufactured articles are of the same age as the fossil bones. In other words, we still require from Africa the same proofs of the existence of links which bind together the sciences of Geology and Archaeology which have recently been developed in Europe. Now, if the unquestioned works of man should be found to be coeval with the remains of fossilized existing animals in Southern Africa, the travelled geographer, who has convinced himself of the ancient condition of its surface, must admit, however unwillingly, that although the black man is of such very remote antiquity, he has been very stationary in civilization and in attaining the arts of life, if he be compared with the Caucasian, the Mongolian, the Red Indian of America, or even with the aborigines of Polynesia." ("The most remarkable proof of the inferiority of the Negro, when compared with the Asiatic, is, that whilst the latter has domesticated the elephant for ages, and rendered it highly useful to man, the Negro has only slaughtered the animal to obtain food or ivory.")