OF THE HALOLIMNIC FAUNA OF LAKE TANGANYIKA. 337 



African Plateau-chain which flanks it on the east. The 

 importance of Lake Tanganyika in a physiographic sense is 

 based largely upon the fact that it lies at the junction of these 

 two very different regions, the latter a disturbed, and the 

 former a quiescent one. As constituting a part of the western 

 arm of the Graben-system, I am inclined to the belief that it is 

 by no means an ancient feature of the earth's crust. Much 

 depends upon the date assigned to the East African volcanic 

 plateau, which was probably initiated towards the close of the 

 Cretaceous period. The Graben-system is of necessity more 

 recent, and if this system has any connection, as regards time, 

 with the Jordan- valley fissure, it must be post-Eocene in date. 

 I think that we may provisionally accept this date for the 

 initiation of the Graben-system, though I should be disposed 

 on other grounds to make it more recent still, bearing in mind 

 that its activities are not yet extinct. 



Lake Tanganyika, as Mr. Moore points out, was formed 

 at different times, but since its existence could not precede 

 that of the Graben-system, the oldest date that we can 

 assign to any portion of it is Middle Tertiary. It is not 

 contended, however, that there were no large lacustrine sheets 

 of a different character at the time of its formation in the 

 neighbourhood, and notably in the area now occupied by the 

 eastern portion of the Congo basin. The geological history of 

 this vast territory is unfortunately a blank since the deposition 

 of the " White Eriable Sandstones." All we can say is that 

 nothing which could indicate the presence of a Jurassic Sea or 

 even of a Cretaceous Sea has been discovered therein. There 

 can be little doubt that the " Ked Felspathic Grits " of Cornet, 

 which underlie the " White Friable Sandstones," may be 

 comprehended under the very wide term of Karoo, wdiich gives 

 us an approximate date. The overlying " White Friable 

 Sandstones " will, therefore, be Mesozoic in age, and probably 

 like the Karoo beds non-marine in origin. 



We now come to the consideration of a very interesting 

 question, viz., the connection between Lake Tanganyika, wdiich 

 is a fissure lake, with the wide and quiescent area of the Congo 

 basin. For several years, as you are aware, geographers were 

 in doubt as to whether Lake Tanganyika had an outlet, and 

 when the outflow of the Lukuga w^as at last established it was 

 thought that the outflow was intermittent. The conditions 

 vary even now, I believe, according to the supply of w^ater in 

 the lake. But what I especially wish to point out is the 

 peculiarity of the Lukuga outlet in a fissure lake surrounded 



