74 THE TANGANYIKA PROBLEM. 



as well)* owing to a general folding and uprising of the 

 earth's surface in this neighbourhood. It would appear 

 further that this sea continued to occupy the vicinity of at 

 least a portion of Tanganyika for a very long time, during 

 which the Drummond series of deposits were laid down as 

 at Masswa, Karema, and on the west coast of Tanganyika 

 near the Luakuga. Another phase of terrestrial activity 

 then occurred, as can be seen by the smashing and faulting 

 of the Drummond beds and more recent formations along 

 many parts of the coast of Tanganyika. It was during 

 these later movements that in all probability Tanganyika 

 became cut off from the sea in the west, and the great 

 lake assumed its modern appearance ; while finally the sea 

 swept still further to the west until it reached its present 

 confines, but owing to the vastness and depth of the 

 Tanganyika fold, the old marine fauna, or at least a 

 part of it, succeeded in surviving in the lake even down 

 to the present day. 



It would also appear, just as in the case of Nyassa, 

 that different parts of the Tanganyika valley have been 

 formed at different times. The central part of Tanganyika, 

 that which stretches between Karema and Ujiji, appears 

 almost unquestionably to be the oldest, while the northern 

 and southern portion are younger additions. This is 

 shown by the fact that only in the middle of the lake have 

 there been laid down deposits which are strictly comparable 

 to the Drummond beds, and which in places have become 

 raised and tilted during the continuation of the folds 



* If we refer to the map facing page 75, it will be seen that the areas of 

 depression in which the old African sandstones occur stretch towards Lake Chiuta on 

 the upper portion of the Lujenda river, and it has been reported to me that shells of 

 one of the remarkable gastropods of Tanganyika are to be found in its vicinity. If 

 this should be substantiated, the above suggestion that the ancient sea at one time 

 occupying the interior of Africa retreated east as well as west would be confirmed. 



