THE TANGANYIKA PROBLEM. 
1 18 
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 iloral characters of a country 
