THE TANGANYIKA PROBLEM. 
45 
north of the present lake, that in this region we first en- 
counter true volcanic action in the shape of a number of 
extinct volcanic cones, with circular craters, and deep blue 
crater-lakes, phenomena which here repeat those to be found 
in the great Tanganyika depression far to the north, and 
again in the floor of the Red Sea itself. 
Portion of the west coast of Lake Nyassa, near Nkata Bay. 
The double cuspecl character of the ridge of the great 
central chain is thus seen to be continued as far as the 
southern extremity of Tanganyika, but at this point a new 
depression of gigantic proportions begins. If we take a 
section through the region of Lake Rukwa, and through 
the southern extremity of Lake Tanganyika from east 
to west (see diagram No. 4), the following physical 
