THE TANGANYIKA PROBLEM. 113 
result that I could find no difference whatever, either in 
its dampness or its consistency, at least, any that it was 
possible to correlate with the different plants that grew 
upon it. In the soil under a great clump of acacias 
there was as little moisture, and it was of the same 
consistency as that upon which there was nothing but a 
scanty covering of grass ; neither can difference of climate 
or rainfall be invoked. Park-lands occur in the Semliki 
valley where it is very wet, and also on the Albert Edward 
plains where it is very dry. 
From general observations, however, it soon becomes 
apparent that park-lands are by no means distributed 
haphazard over the surface of the country ; they never 
occur, for example, on hill sides or upon rocky ground. 
They are invariably found upon alluvial plains like those 
formed by rivers, or upon old lake deposits ; that is, they 
only occur on flats made up either of blown sand or 
of ground of aqueous origin ; but although they are 
definitely related to fiats of the above sorts, this fact at 
first sight perhaps makes the whole matter more perplexing- 
still, for such flats are by no means invariably covered 
with parks. Thus there are wide districts on the Semliki 
plains which are covered with heavy forest, and there are 
similar alluvial areas covered with heavy forest only along 
the Zambesi river, and indeed in many places elsewhere. 
What can it be, then, which in some places inaugurates 
and maintains a natural African park ? This question is a 
great puzzle, and the answer to it is not at all apparent on 
the surface of things. I obtained, however, what there is 
every reason to believe is a clue to the whole matter, during 
my visit to the Albert Nyanza. On that journey I 
descended from the western slopes of the Mountains of the 
Moon on to the plains of the great central valley, which I 
8 
