THE TANGANYIKA PROBLEM. 
123 
also not wanting indications that Nyassa was at one time 
directly connected with Lake Shirwa, and it is probable 
that at some more remote period both these lakes as one 
threw their surplus water down the valley of Lujenda River. 
Besides general falls in the level of Nyassa, there are, 
however, indications of local disturbances of level, such as 
those to which I have referred in Chapter III., and these 
changes are undoubtedly due to the geological distortion 
which is still going on along the course of the Great Central 
African Range, within the folds of which Nyassa lies. The 
floor of the lake valley is very deep indeed, reaching we 
found in one place 430 fathoms, and these results have 
been subsequently closely confirmed by my friend Lieu- 
tenant Rhoades. Over large areas, generally, in fact, 
the floor of the lake is as low and lower than the sea 
level ; and consequently we may say broadly that the lake 
valley is a chasm, or fold, in the earth’s surface over 300 
miles long and about 50 miles broad, and 10,000 to 11,000 
feet deep. Owing to its latitude the climate of Nyassa 
is warm and tropical, but since the lake’s surface is 1,500 
feet above the sea level, the monotonous heat experienced 
on the equatorial African sea coasts is perceptibly tem- 
pered, especially at night. 
Observations have been made on the fauna of Nyassa by 
a number of explorers, by Sir John Kirk, Livingstone, 
Joseph Thomson, Mr. Crawshay and others, and in 1895 
and 1899 extensive examinations of the lake were made by 
myself and my colleagues during the Tanganyika expedi- 
tions. The investigations undertaken during both these 
journeys extended over three months, and the results 
obtained throughout all the different regions of the lake 
which we examined were of such a definite and similar 
character that there can be no doubt we have pretty well 
