THE TANGANYIKA PROBLEM. 55 



still going on. Were Africa, as it was at one time 

 supposed to be, an ancient granitoid land-mass, without 

 aqueous deposits of any kind on its surface beyond those 

 of local lakes and marshes, we might show that the earth 

 movements giving rise to its present form had been 

 maintained through a lengthy period. But we could find 

 no evidence which would be of any value in fixing the 

 chronological relationships of the different outbursts of 

 activity which have taken place in different parts of the 

 area ; nor should we be able to form any clear conception 

 of the configuration which the continent might have 

 possessed in ancient times. The gradual discovery by 

 Speke and Grant, by Drummond,* Cornet, t and ourselves, 

 of extensive aqueous deposits of different ages and character, 

 which cover enormous areas of the interior and are of 

 enormous depth, have, however, completely altered the 

 possible results to be obtained from a study of the geology 

 of the African interior. By an examination of the nature 

 of these beds, of the relationships which they bear one 

 to another, and by the study of the manner in which they 

 have been affected by the successive earth movements 

 which have taken place, it is even now possible to throw 

 some light upon this hitherto mysterious and enigmatical 

 land-mass, and, at any rate, to show that its past history is 

 not at all in unison with existing theoretical anticipations. 



As by far the most extended and continuous geological 

 studies of the African interior which have hitherto been 

 made are those which were undertaken during the first, 

 and especially by my colleague, Mr. Fergusson, during the 

 second Tanganyika expeditions, it will be convenient to 

 deal primarily with the facts recorded during these two 



* Tropical Africa. 



t J. Comet La Ge"ologie du Bassin du Congo, Le Mouvement Geogr. 1897, Bd. H- 



