4o6 



NA TURE 



[August 25, \\ 



Halolimnic forms naturally excites, is not necessarily restricted 

 to the particular basin in which Tanganyika lies ; indeed, we 

 have to thank Prof. Siiss^ for collecting the existing observations 

 in such a manner that we are now not only able to separate the 

 lakes into two distinct series, of which the Victoria Nyanza 

 and Tanganyika are types respectively, but to show clearly that 

 the singular Tanganyika valley is geologically related to the 

 similar valleys in which numerous other long and narrow lakes 

 are found to lie. Siiss showed that the continued existence of 



Fig. 1. — Sketch map of the Great Lake region of Africa, showing the relation of the principal 

 lakes to the Chains of Rift valleys; and the distribution of the normal fresh-water and 

 Halolimnic fauna in these lakes. The lakes partially shaded are those which have not 

 yet been zoologically explored, and in which the Halolimnic fauna may be found. The 

 one Lake Tanganyika, in which the Halolimnic fauna is now definitely known to coexist 

 with the ordinary freshwater stock, is represented quite black ; while those lakes, such as 

 Nyassa, in which there are certainly no marine forms, are left entirely white. 



these valleys could be traced north and south in Africa, from 

 the Nyassa region to the Red Sea, and that the narrow gulf in 

 which the Red Sea is itself contained, must be regarded as of 

 the same nature and construction. 



Now the fact that there exists a marine fauna in Tanganyika, 



at the one extremity of the same series of valleys in which the 



Red Sea lies at the other, would rather lead us to expect that we 



may encounter the Halolimnic fauna, or something similar to it, 



1 " Die Brucke des Ost Afrika." 



NO. 1504, VOL. 58] 



in the Albert Edward and Albert Nyanza, which lie along the 

 .same depressions in between. 



The facts of distribution which have actually been obtained 

 are, however, merely these. I showed that the Halolimnic 

 fauna does not exist in Lake Nyassa, nor in any of the sub- 

 sidiary lakes which occur within the British Central African 

 Protectorate. It is, further, certain that this fauna does not exist 

 in Mwero or Bangweolo, the two lakes which form the western 

 boundary of North Charterland. 



In the accompanying map, these lakes 

 are therefore represented blank. It may, 

 however, be yet found in Rukwa, east 

 of Tanganyika (which is consequently 

 shaded), and it is still more likely to 

 occur in Lake Kivu, the Albert Edward, 

 and the Albert Nyanzas, all of which lie 

 actually in the same valley as Tanganyika, 

 immediately to the north, and concerning 

 the fauna of which practically nothing is 

 known. 



Passing to the more westerly series ot 

 faults, it is certain from the collections 

 of shells brought back by Dr. Gregory 

 from the small lakes Naivasha, Elineteita 

 and Baringo, that the Halolimnic fauna 

 is not present in these districts, while 

 the collections of Messrs. Donaldson 

 Smith and Cavendish, from Lake Rudolf 

 in the north, seem to tell the same 

 story.^ It would appear therefore, that 

 unless some marine extension formerly 

 existed, which was quite independent 

 of the Rift valleys, up some such de- 

 pression as that of the RuSgi and 

 Ulanga rivers, in which case the remains 

 thereof will be exceedingly difficult to 

 find, both the living and dead repre- 

 sentatives of the Halolimnic group, may 

 be expected in the great depression north 

 of Tanganyika, i.e. in the three lakes 

 which I have named. Mr. Scott-Elliot, 

 who descended into the northerly exten- 

 sion of the Tanganyika valley, between 

 Ruanda and Mwezi's country, speaks of 

 old lake-bottoms occcurring there above 

 the present level of Tanganyika, as sandy 

 plains, with banks of drifted shells ! An 

 immense amount of interest, therefore, 

 attaches to the exploration of these lake- 

 bearing districts immediately to the north 

 of Tanganyika. > 



Referring to the map, I would there- 

 fore direct special attention to the fact 

 that Lake Kivu Is about four days' march 

 from the extreme north of Tanganyika, 

 along the same valley and up the lake's 

 etifluent, which flows back into the Tan- 

 ganyika basin. From Kivu it is certainly 

 not more than five days' journey to the 

 Albert Edward, which is on the other 

 side of the north and south watershed, 

 and overflows into the Nile. The 

 effluent appears, so far as I can ascertain, 

 to be navigable for boats ; and if this be 

 so, the Albert Nyanza could be reached 

 without trouble in five or six days.; in 

 any case, and allowing ampl-e time for 

 zoological work in these lakes, the 

 whole series could be explored, in. 

 something less than two months from 

 the time of leaving the north of Tan- 

 ganyika, and all that it would be necessary to take in. order to 

 do as much as, and a good deal more than I have already 

 done in the case of Tanganyika, would be a few suitable dredges 

 and a couple of collapsible boats. 



There is, however, another direction in which evidence 

 bearing upon these subjects can be sought. At the present time the 

 geology of this part of the African interior is almost entirely a 



1 I have, however, shaded Rudolf, as very little is known about the 

 fauna it ontains. 



