8 4 
THE TANGANYIKA PROBLEM. 
these, in like manner, contain the peculiar papyrus- 
swamps, which characterise a large portion of central and 
east-central Africa. They are, in fact, the so-called rush- 
drains of Sir Henry Stanley, and of which Mr. Scott 
Elliot so aptly remarks, “ they hardly ever contain rushes 
and nearly always require draining.” 
The one peculiar geological feature which the Kivu 
valley represents, is due to the fact that the waters of the 
lake are charged with saline matter to such an extent that 
the shores have become incrusted with a singular material, 
containing a high percentage of magnesium carbonate. 
Samples of this incrustation from the water of the lake, 
obtained by Mr. Fergusson, were examined under the 
direction of Professor Wynne, at the Royal College of 
Science, and “from analyses made by Mr. J. Hart-Smith, 
F.R.C.S., it is evident that magnesium replaces calcium in 
the water ; the analytical and spectroscopic evidence 
showing that traces, only, of calcium salts are present. 
Fragments, obtained from the lake floor, consisted of a 
calcareous tufa, evidently deposited round vegetable debris ; 
and when analysed by Mr. W. Robinson, A.R.C.S., were 
found to contain CaO, 28’65, MgO, I2'66 per cent., as a 
mean of two closely agreeing analyses.” This substance 
gathers about the objects on the shore line, incrusting the 
pebbles and the reed- stems in such a manner, that extra- 
ordinary nodular masses of incrustation are formed, which 
are as hard as Roman cement. The incrustation also 
encloses the shells of the few molluscs which exist in Kivu, 
and has often during its formation been pierced with old 
reed-stems in such a way, that the long parallel tunnels, 
which once enclosed the stems, look as if they had been 
bored by some species of pho/as , until their actual nature has 
been ascertained. 
