It is hardly conceivable that any geographer should have admitted an hypothesis, the absurdity of which must have been manifest upon the slightest reflection. The height of lake Tchad has been ascertained: it is nine hundred and twenty French feet above the level of the sea, or something less than three hundred metres; it cannot, therefore, receive the waters which flow to Funda.
The course of this river east of Funda must be reversed, and the supposed elbow converted into a tributary: we shall then probably approach the truth. Major Denham was the first to conceive this easterly turn of the river, running north of the great chain of mountains, and falling at a great distance into the central lake; he had been assured that a communication existed between this river and lake Tchad by the Chary. How is it that the physical impossibility of this course did not occur to him?
A very simple consideration appears to afford a solution of this difficulty, namely, the existence of a lake in an elevated point of the Mandara chain, giving rise both to the Chary and the river which flows by Adamowa and Djacoba. The reports made to Major Denham demonstrate the importance of this stream, which is sufficiently proved by its extent; but, why, without ocular testimony, did he imagine its course to be easterly? If the negroes did not inform him that it ran to the west, neither did they state the contrary. Let us admit the westerly direction: a certain communication will then exist also between the Couara and the Chary; only, after having descended a current southwards, we must ascend another eastward, and thence redescend northwards, into the central lake. This is the most plausible theory I can devise upon Major Denham’s opinion; this is nearly the case with the White Nile and the Misselad, both taking their rise in one of the lakes of Gebel-Koumri. Upon this system, the Couara will continue, after the confluence, to flow southwards, and fall into the sea near the coast of Benin.
A fifth opinion has been recently broached by the English General Sir Rufane Donkin;[142] the summary of which is that the Niger crosses the Wangarah, enters the valley of Ouadi-el-Ghazel, formed by the continuation of the Misselad, and thence runs into the Mediterranean (in the great Syrtis) by a subterranean channel under the sands of Bilmah; and moreover that the Niger rises near the Gulph of Guinea, instead of running towards it. This rather extraordinary opinion has met with adversaries, at which we need not be surprised, even after having read the arguments on which the dissertation is founded. I do not therefore think it necessary to discuss it here; neither shall I enter into the complicated notions, upon the courses of the central river, hazarded by the English traveller Bowdich on very vague information; and I shall be cautious not to offer an additional hypothesis of my own respecting this problem, still full of obscurity. On what basis can an entire and complete system be founded while even the names of the central regions are unknown to us, and our researches into the physical geography of these vast tracts are yet in their infancy; when, in short, the papers of Major Laing, should they be recovered, may at once throw strong light on these chasms in science?[143] It may however be affirmed, and I think with certainty, that the rivers called Dhioliba and Couara neither join the Egyptian Nile, nor contribute one drop to its waters; I think besides that, if the Couara of Funda actually is the continuation of the Dhioliba, flowing to Sego and Timbuctoo, and falls into the Gulph of Guinea, there is nothing to hinder it from throwing off a branch to the east, which may have its outlet in the Yeou and the central lake: this would be the branch seen by M. Caillié before he reached Timbuctoo, and which our traveller followed, the other being on his right flowing east-south-east; and there is no proof that the whole of the former rejoins the latter. The great lake Tchad, or central sea, would then not be the general receptacle of the Dhioliba, but only one of its outlets.
CHAPTER II.
VOCABULARIES COLLECTED BY M. CAILLIÉ.
Compared with those of Mungo Park, Bowdich, Jackson, Denham, &c.
1.