THE TANGANYIKA PROBLEM. 
Si 
the lake. On the lake shore, at certain places, Viuwko and 
Lumungi, the sandstones were found to rest on granite, 
which can be seen just above the present water-line ; but 
north of Lumungi the sandstone deposits disappear, and 
are succeeded by granites, gneiss and schists, which form 
the chief constituents of the great mountain range flanking 
the extreme north of Tanganyika on the east, and which 
can be seen running away north, parallel with the similar, 
but even higher, range encircling the lake to the west as 
far as the eye can see. 
At several points on the shore of Tanganyika, between 
Ujiji and Usambora, at the extreme north end of the lake, 
I found, under these great sandstone scarps, layers of 
modern, broken lake deposit lying with the same dip, about 
20° to the east, as the sheets of old sandstone on which 
they rested. These modern lake-beds are now ioo 
feet above the water-line, and contain the same peculiar 
halolimnic shells which are now found inhabiting the lake ; 
but they are broken and upraised abruptly from the 
present floor of the lake along a line of faulting parallel to 
the shore, this fact in itself showing that the general 
upheaval, which has thrust the old sandstones 10,000 feet 
into the air along the east coast, is still going vigorously on. 
We found, on nearing the north end of Lake Tan- 
ganyika, that the great valley in which the lake lies 
(deeply enclosed by lofty, green hills) could be seen ex- 
tending as a flat-bottomed trough, far beyond the northern 
shore ; and we found also that the flat floor of this valley, 
after leaving Kajagga, near the inflowing Rusisi River 
(which comes from Kivu and opens by five mouths into the 
lake), was composed chiefly of modern sandstones and 
alluvium. At first the flat floor of the valley was covered 
with coarse grass and reeds ; but, as we rose slowly from 
6 
