44 
THE TANGANYIKA PROBLEM. 
of this nature has gone on ; and the only further demon- 
stration which is required to make the tale complete are 
some observations which will show that the floor of the valley 
of Nyassa has become, or is becoming, actually thrust down. 
Such evidence is readily to be obtained at the north end of 
the lake. The water of Nyassa has fallen many feet within 
no great number of years, and in consequence, wide plains 
of old lake deposit and alluvium covering what was once its 
door have become dry land near Karonga and further north. 
At the end of 1895, when I first visited the lake, the water 
of Nyassa was shown by observations made by the officers 
of the gunboats to be lower on the whole than it had been 
for many years ; but notwithstanding this, I was shown to 
my intense surprise a number of old trees not far from 
Karonga, which were standing about two hundred yards 
in the water of the lake, and the trunks of which were 
then submerged some five feet. Moreover, the old natives 
of the district, whom Dr. Cross interrogated on this subject 
for me, assured us that they could remember a time when it 
was possible to walk out to these same trees, which were 
then not near the water at all, and at whatever rate the 
change in level has taken place, it is quite clear that it can 
only have been produced by local subsidence of the ground, 
i.e.j by the sinking of the floor of the Nyassa Valley during 
the life of these particular trees. 
The valley of Nyassa, like that of Tanganyika, is continued 
beyond the lake to the north (see map, opposite p. 48), and 
although its magnitude becomes lessened and partially filled 
up, there is no doubt that the individuality of the depression 
can be traced as far north as the valley of Lake Rukwa, 
which lies to the east of the Tanganyika depression, but 
finally runs into and crosses it obliquely from east to west. 
It is in the floor of the Nyassa depression, some way to the 
