280 A NATURALIST IN MID-AFRICA. 



from my own observations, I cannot conceive for 

 what possible reason any such theory should have 

 been published. There is no geological difference 

 between the northern and southern half, and no 

 reason to suppose that the lake is not what it 

 appears to be, namely, a rift valley like that of 

 the Man. It is, in fact, simply a pool on the 

 Upper Congo region. 



The changes of level may be most simply 

 explained by the supposition that the outlet by 

 the Lukuga is in some places extremely narrow 7 

 and liable to be blocked. 



Data for ascertaining the changes of level — 

 due probably to the opening or closing of this 

 outlet — may be obtained from three sources. 



There is first the obvious difference between 

 Captain Hore's careful map and the present 

 outline of the shore. There is also the height 

 of the occasional alluvial plains, e.g., that about 

 Karemi ; and there is, finally, the level of the 

 white incrustation due to the deposit of saline 

 matters from the water on the rocks near the 

 lake. 



From observing these points I was able to be 

 sure of one fact, that the level of the lake was 

 at one time 21 feet higher than its present con- 

 dition. It appeared to me very unlikely that this 

 high level could have been maintained for a long 

 period. 



For the last three years the level has been 



