84 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 ol 

 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, 12*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 ftkolas, until their actual nature has 

 been ascertained. 



