n8 THE TANGANYIKA PROBLEM. 



also indicative of change in one particular direction — that 

 is, of the gradual drying up and shrinking of whatever 

 lakes and open waters the district may possess. Hence the 

 almost universal distribution of park-lands all over Central 

 Africa is clearly indicative of one of two things : either the 

 rainfall is becoming less over the whole of the equatorial 

 regions, or the land is being gradually moved and changed 

 and shifted in such a manner that the water on it is being 

 drained off the interior as a whole. There is no evidence 

 of any decrease in the rainfall, but as we have seen there 

 is abundant evidence of continuing geological change ; and 

 therefore we are driven to conclude that the existence 

 of these extensive parks must be due to movements and 

 shifting in the watersheds, and the general configuration of 

 the land. Now, the only direction in which earth move- 

 ments on a slow and extensive scale could effect this 

 draining, is by that of a gradual raising and humping up 

 of the interior ; and it is extremely interesting to find that 

 the study of the features of natural parks, thus leads exactly 

 to the same conclusion respecting the impermanence of the 

 terrestrial conditions of the interior, that were indicated 

 by the geological and physiographical considerations which 

 I discussed in the last chapter. 



Although it will thus be seen that the history of African 

 park-lands affords us another mode of demonstrating the 

 geological impermanence of the African interior, and of 

 the existence of a progressive series of physical changes 

 which are still going on there, it should not be overlooked 

 that their history is also not without a rather wide im- 

 portance from a purely biological point of view. It teaches 

 us in an analogous way to the matters connected with the 

 formation of fresh-water faunas in general, which I described 

 in Chapter II., that the main floral characters of a country 



