OF THE COURSE OF THE DHIOLIBA ABOVE AND BELOW TIMBUCTOO.
The attentive reader who may have patiently followed me through the preceding pages, will, no doubt, have remarked the new and principal fact which results from M. Caillié’s observations; the division of the Dhioliba in the environs of Sego into two branches equally broad and deep, and the existence of a large island. It elucidates the description of Mungo Park, and reconciles him with our traveller; it explains the contradictions between the situations assigned to the same towns by different travellers, sometimes on the right, and sometimes on the left of the river, and finally it enlarges our ideas of the advantages of navigation in the interior of the Soudan. This fact also accounts for the great collection of waters which forms the lake Dhiebou or Debo, because many considerable branches which separate from the western arm unite again with the main stream beyond the tributary which falls into it at Isaca; and the want of declivity in the direction of this junction is the cause of the stagnation of the waters.
It would appear that the river has different names which change with its course. Called at its source Tombia, Ba, Dhioliba, &c., it retains the latter name as far as Sego, where or in the environs it divides; if we may trust the description of the amanuensis of Bello, the left arm is called Baniou, and the right Balio, and after the junction it is called only Couara. But M. Caillié never once heard that the river, which he reached at Galia, and upon which he navigated thirty days, had different names; perhaps because he did not inquire. He only saw a river, Couaraba, which falls into the right branch, but very far to the south. I think then that if the stream is called Couara below Isaca, it is only because the term is generic and signifies a river.
I might stop here and leave it to the reader to draw other consequences from the new observations. But the question of the outlet of this stream is so closely connected with my subject, that the reader would have a right to complain if in this work he found neither information nor opinion upon it. It is universally inquired what becomes of this immense collection of water below Timbuctoo; it is at least necessary to exhibit in a few words the different opinions at present current upon this subject.
The most ancient identifies this river with the Nile of Egypt. It does not appear that the partisans of this opinion had any other foundation than the pretended unanimous reports of blacks, Arabs, and natives. Thus without considering the physical conditions, or taking account of insurmountable obstacles, they maintained as a fact, that the waters which had their rise in the heights of the Soulimana, that is to say at an elevation of from fourteen to fifteen hundred feet, reached the Mediterranean after a course of two thousand leagues. But, what is perhaps still more strange, this notion rested wholly upon the equivocal interpretation of a word, or as we may express it in plain English upon a pun; the word Nile or Nil is generic. In saying that the Dhioliba joins the Nile, the Africans mean no more than it communicates with some other great water, whether it falls into it, or whether it receives it, (for this distinction of arm or tributary is very important). When therefore the Arabs say that the Dhioliba communicates with the Nile or the Bahi, they understand thereby either a great river, or a sea, and this may be an inland sea as well as the Ocean. This opinion that the Dhioliba empties itself into the Nile of Egypt, though it was supported only a few years since by a learned writer, appears to be now altogether abandoned.
But this is not the case with the opinion of those who, like Major Rennell, consider the central lake as the outlet of the river. Before the discovery of the lake Tchâd by the English travellers, the existence of this inland sea might have been doubted, the evidence of it was so vaguely attested. This opinion, however supported by probability, is nevertheless liable to two objections: first, that upon the whole western coast of the lake is found the mouth of only one inconsiderable river, the source of which is at no great distance in the E. S. E.; secondly, that the town of Boussa, to which Park navigated upon the Dhioliba, is now known by the second journey of Clapperton, and that it is very far to the S. E. of Timbuctoo.
With regard to the first objection, it may not prove a serious difficulty, because recent travellers have not followed the river Yéou, which falls into lake Tchad; they have left it at a certain distance from the lake, and it is very possible, that that which they have seen farther on may have been only a tributary to the former. As to the second objection, it might be more important if it were certain that the Dhioliba runs in a single bed from Timbuctoo to Saccatou and to Boussa; but there is nothing to prove this. Continuing eastwards, towards the central lake, it may send out a branch to Boussa; and this division would account for the Yéou consisting of but an inconsiderable body of water.[136]
Reichard was one of the first who imagined that the Dhioliba may run into the Gulf of Guinea. This hypothesis has for some time past assumed a certain degree of probability, to which the opinions of the later English travellers, Clapperton and Major Laing,[137] have added much weight. They differ, however, respecting the outlet of the river: the one preferring the river Benin (or Formosa), with Reichard[138]; the other, but with much less probability, the Rio-Volta. The objection always raised to this hypothesis is the great height of the mountains called Kong. To reach the sea, the river must cross them; but it may not be absolutely impossible that there should exist an opening in them deep enough to admit of its passage. Another difficulty arises from the small declivity of these waters: but I will here make an observation on this subject. The actually known course of the Dhioliba, from its source as far as Timbuctoo, is about three hundred and sixty leagues: it issues from Mount Loma, at a height of nearly sixteen hundred English feet above the sea, or less than five hundred metres. The velocity observed by M. Caillié leads to the belief, that the average inclination from Djenné and also from Bamakou to Timbuctoo is two thirds of a metre to a league: Timbuctoo would stand, according to this datum only, at a height of two hundred and sixty metres; but it is very probable, that the inclination is much greater from Mount Loma to Bamakou than it is below this latter point, which would lower the position of Timbuctoo at least to two hundred and thirty metres, taking the fall of the first part at only a metre for a league. But this quantity would greatly exceed that supposed by Capt. Beaufort, who, after having observed the elevation of Elimané, conceived Timbuctoo to be upon the same level, that is to say, eighty-four metres above the sea.[139]
Now, from Timbuctoo to the mouth of the river of Benin, following the course of the waters (as it is traced by the partisans of this opinion), the distance is not less than four hundred and sixty leagues. Thus, in the second part of its course, the river would have a total declivity of 230 metres, or 0,51 metre to a league. It is known that the Seine has an inclination of 0,72 metre to a league; the Mississipi, 0,84 metre; the Rio-Apure, 0,92 metre, &c. but others have a much less fall, such as the Wolga, the Missouri, the Senegal, &c., which have one of 0,50 only;[140] so that, strictly speaking, the above inclination is sufficient.
According to a fourth opinion, the river, on reaching the Kong mountains, makes an elbow to the left and runs eastward, by Djacoba and Adamowa to Chary, and thence to lake Tchad into which it discharges itself. It is here that the objection of the want of sufficient inclination applies: how can it be admitted, that the river, after passing Funda, where it would scarcely have an elevation of fifty metres[141] above the sea, (supposing it to be the river of Timbuctoo which flows to Funda), can run on to lake Tchad, three hundred and fifty leagues farther, through a country represented by all accounts as mountainous? But this, even, is not the greatest difficulty.