802 W. H. HUDLESTON, ESQ.^ M.A., F.R.S., ON THE ORIGIN 



which their authors have drawn, it must be with bated breath 

 and with the full consciousness ever present in our minds that 

 they have been there and that we have not. In the light of 

 so much that has i ecently been revealed, it is only natural that 

 many controversies should arise, and some of these perhaps 

 may be ultimately settled by more extended investigations 

 leading to further knowledge of the subject. As a case in 

 point, I may mention the remarkable circumstance which has 

 greatly exercised the minds of certain zoologists, viz. : — that 

 there are some species of fishes in the waters of the Upper 

 Nile which also occur in the hydrographic basin of the Jordan 

 in Palestine, and yet are not found in the waters of the Lower 

 Nile in Egypt. When zoologists are desirous of accounting for 

 anything which seems abnormal or difficult of explanation, 

 they are quite prepared to make the earth's surface undergo 

 considerable modifications in order to suit their special line of 

 argument, and indeed they can generally find a sufficient 

 number of geologists to back them in such a course. This 

 subject may crop up again when we proceed to consider the 

 geological structure of eastern Equatorial Africa, and, there- 

 fore, it will be sufficient at the present moment merely to refer 

 to the hypothesis, which connects the drainage of the Jordan 

 system, through the Gulf of Akabah and the valley of the Eed 

 Sea, then supposed to be a fresh-water river, with a portion of 

 the " Eift Valley" system, and ultimately with the drainage 

 of the Upper Nile. Far be it from me to say that such an 

 explanation is incorrect, but it certainly ignores all existing 

 hydrographic arrangements most completely.* 



The case I have just quoted is perhaps more difficult of 

 solution than the problem which we are now called upon more 

 especially to consider, viz. : — the origin of the halolimnic fauna 

 of Lake Tanganyika, or in other words what Mr. Moore very 

 aptly calls the "Tanganyika Problem." In attempting to 

 grapple with this very curious and interesting question, be- 

 sides the zoological evidence, it will be necessary to consider 

 the geological structure of Equatorial Africa as far as the scanty 

 details of our present knov/ledge permit ; and if we venture in 

 this connection to attempt to trace any portion of its physical 

 history in times past, such reconstruction should harmonize as 

 much as possible with known facts and existing features. 



On this subject the reader is referred to a paper " On the physical 

 conditions of the Mediterranean Basin, which have given rise to a 

 community of some species of fresh-water species in the Nile and in the 

 Jordan Basins." T vans. Vict. Inst., vol. xxxi, p. 3 (with map). — E. H. (Ed.) 



