74 
THE TANGANYIKA /'ROT LEM. 
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. 
