72 
THE TANGANYIKA T ROB LEM. 
whole region, and subsequently possibly another sinking, but 
after a lapse of unknown duration, the less extensive aqueous 
deposits, constituting the Drummond series, were deposited 
inconformably over the top of the old African sandstones. 
In these latter beds there are, as we have seen, the remains 
of several ganoid fishes, which, according to Professor 
Traquair, are similar to, but specifically distinct from, the 
existing African species. Now the interest in this matter 
lies in the fact that the existing African polypteroids do not 
occur in Nyassa, nor in any of the existing rivers of this 
region, nor in fact anywhere south of the Congo watershed. 
The shells which were found in the Drummond beds tell 
the same story, being more or less similar to but not quite 
like the Lamellibranchs at present found in Tanganyika. 
On referring to Professor Gregory’s* general, account of what 
was known of the geology of Central Africa in 1895, we 
find reference made on page 230 to the further remarkable 
fact that the fossilised remains of an oligocene echinoderm 
appear to have been brought from the neighbourhood of 
north Nyassa, and from this Professor Gregory argues, with 
much apparent reason, that there must have been an exten- 
sion of a comparatively recent sea into this portion of the 
African interior. 
It would thus appear that at some time there was in this 
region a fauna consisting at any rate of ganoid fishes, 
echinoderms and molluscs ; or, in other words, a marine 
fauna, and that these things entirely disappeared through 
the great physical changes and displacement which occurred 
during the extension of the Nyassa fold into this par- 
ticular area. There is no vestige of a marine relic in 
the Nyassa fauna of to-day, and it would consequently 
appear that Nyassa extended into this region only after 
* “ The Great Rift Valley.” 
