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,! 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. Cornel La Geologic du Bassin du Congo , I.e Mouvement Gcogr. 1897, Bd. 14. 
