082 Bulletin American Museum of Natural History [Vol. LIIT 
time, as is quite probable, they became more saline than at present and 
such past conditions of salinity may have influenced the nature and evolu- 
‘tion of the fauna. At some comparatively very recent epoch, perhaps 
during the Pleistocene, the formation of the Mfumbiro Volcanoes diverted 
the waters of Lake Kivu from the basin of the Nile, to which they formerly 
flowed, southward into Tanganyika. This additional supply slowly 
raised the level, so that the Lukuga was eventually again opened up as 
an outlet. The lake at first sank rapidly and its level later became sub- 
ject to fluctuations with the time of year and the amount of rainfall. 
There are observations on record showing a certain periodicity in the rise 
and fall of the level even since the relatively recent arrival of Europeans. 
At the time of Cameron’s visit in 1874 and of Stanley’s in 1876, the 
waters were beginning to filter through the outlet of the Lukuga at the 
end of the rainy season and for a number of years, about that time, the 
outflow may have been intermittent. About 1879 a definite channel was 
opened, the outflowing water sufficing to sweep away the alluvial silt and 
obstructing water plants. The consequent lowering of level in Tangan- 
yika during the ensuing years appears to have amounted to about 11 m., 
and the lowest level was reached, it seems, about 1894, when a general 
rise set in, reaching its maximum in 1917. Since, a renewed fall has been 
recorded. It has also been contended that Tanganyika undergoes a 
gradual desiccation through evaporation or reduction of inflow, but the 
regulating function of the Lukuga appears to be quiet sufficient to 
explain the observed fluctuations of level. 7 
In connection with the fluctuations of level of Tanganyika it is 
worthy of mention that at various places there are shore deposits of shells 
apparently belonging to species still living in the lake. Some “were 
found embedded in a coarse, sandy matrix upon the shore at Sumbua, 
about halfway up the east coast of the lake. One reef was so weathered 
that the shells (Neothauma) stood out very conspicuously, just in the 
breakers. Three similar reefs occur at intervals inland, on the summits 
of the former sandy beaches. These shells may be referred to a late 
Post-Pliocene age. Other specimens occurred in a cliff or ridge, about 
six feet high, in the northwest part of the Rukwa Valley, where the lake 
formerly was, but is now dried up. So far as one can judge, none of the 
shells which are more or less perfect, or of those of which there are only 
fragments, belong to other than recent species, showing that these ridges 
are of quite modern origin. Among those from Sumbua, besides the 
Neothauma, are remains of Rumella, a thalassoid genus, and of Unio; 
and from the Rukwa Valley are fragments of Lamistes, Vivipara, Melania, 
