1927] : Pilsbry-Bequaert, The Aquatic Mollusks of the Belgian Congo 579 
Lake Kivu 
Lake Kivu lies in the Albertine Rift about 110 kilometers north of 
Tanganyika, at an altitude of 1,460m. Ina north to south direction it is 
some 100 kilometers long and, from east to west, 50 kilometers wide in 
the middle, covering an area of approximately 2,650 square kilometers. 
It contains several islands, most of them of small size. The largest, that 
of Kwidjwi, is over 40 kilometers long, situated near the southern end, and 
traversed by a hilly, rocky ridge. The shore is steep everywhere, often 
rising in cliffs, with many fjord-like indentations. The deep, blue 
waters, which have not been properly sounded, contrast with the white, 
crust-like deposit of mineral matter on the rocky shore.! The water is 
remarkable for the excessive quantity of saline matter it contains, espe- 
cially a very unusual amount of salts of sodium and magnesium, there 
being more than twice the amount of salts of magnesium present in 
Tanganyika. On the other hand, the water appears to be almost entirely 
free of calcium salts.2 In addition, it contains a slight proportion of 
sulphuretted hydrogen (one part in 100,000) and a certain quantity of 
boric acid, probably present as magnesium borate. The presence of free 
sulphuretted hydrogen in solution shows that most of the oxygen has been 
eliminated to form various sulphates. There are a number of hot springs 
in the lake, while occasionally bubbles of oil come up suddenly, forming 
black patches on the surface. The lake, being quite deep, is often agitated 
by violent tempests. It should also be mentioned that, when the 
Namlagira voleano is in activity, the water of the northern part often 
reaches such a high temperature that many of the animals die; this being 
due either to submarine eruptions or to lava flowing into the lake. The 
watershed of Kivu is very small, since no sizable rivers flow into it. 
At the extreme southern end the lake flows out to Tanganyika, by way 
of the Ruzizi, a narrow, rocky mountain stream.° 
The peculiar physical and chemical features of Lake Kivu account 
sufficiently for the extreme poverty of its plant and animal life, which 
are especially handicapped by the unusual high salinity. Only thirteen 
1According to J. E. S. Moore (1903, ‘The Tanganyika problem,’ p. 84), analysis of samples of these 
shore incrustations showed them to contain 26.65 per cent of CaO and 12.66 per cent of MgO. “This 
substance,” he says, ‘‘gathers about the objects on the shore line, incrusting the pebbles and the reed- 
stems in such a manner, that extraordinary masses of incrustation are formed, which are as hard as 
Roman cement. The incrustation also encloses the shells of the few mollusks which exist in Kivu.” The 
shells we have seen from Kivu were, however, quite free of incrustation. : x 
2See Hundeshagen, F. 1909. ‘Analyse einiger ostafrikanischer WAasser.’ Zeitschr. Offentl. Chemie, 
201. 
3Further details concerning the physiography of Lake Kivu are to be found in Bockelmann, A. V. 
1901-02. ‘Versuch einer Monographie des Kivu-Sees und seiner Umgebung als Begleittext zur Dr. 
Kandt’s Karte.’ Beitr. Kolonialpolit. u. Kolonialwirtsch., III, p. 357, map. eee 
Kandt, R. 1905. ‘Caput Nili. Eine empfindsame Reise zu den Quellen des Nils.’ (Berlin), 
2d Ed., xvi +538 pp., 12 Pls., 1 Map. 
