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 cusped 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 



