72 THE TANGANYIKA PROBLEM. 



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." 



