The Tanganyika problem; an account of the researches undertaken concerning the existence of marine animals in Central Africa . Diagram IV -Section through Lakes Tanganyika and Rukwa from North-East to North-West. Vertical scale X 5. page 44. 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 ofextinct volcanic cones, with circular craters, and deep bluecrater-lakes, phenomena which here repeat those to be foundin the great Tanganyika depression far to the north, andagain in the floor of the Red Sea itself.
The Tanganyika problem; an account of the researches undertaken concerning the existence of marine animals in Central Africa . Diagram IV -Section through Lakes Tanganyika and Rukwa from North-East to North-West. Vertical scale X 5. page 44. 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 ofextinct volcanic cones, with circular craters, and deep bluecrater-lakes, phenomena which here repeat those to be foundin the great Tanganyika depression far to the north, andagain in the floor of the Red Sea Portion of the west coast of Lake Nyassa, near Nkata Bay. The double cusped character of the ridge of the greatcentral chain is thus seen to be continued as far as thesouthern extremity of Tanganyika, but at this point a newdepression of gigantic proportions begins. If we take asection through the region of Lake Rukwa, and throughthe southern extremity of Lake Tanganyika from eastto west (see diagram No. 4), the following physical 46 THE TANGANYIKA PROBLEM. phenomena are apparent :—The country rises towardsthe eastern scarps which flank the trough-like de-pression of Lake Rukwa, where a line of faultingoccurs. At the base of these eastern cliffs, which werefound by Mr. Wallace to be about 400 feet in height,there is a flat, dusty plain of modern lake deposit, andthen another series of scarps facing those on the eastand marking another parallel line of faults. Above thesewestern scarps of the Rukwa depression the land risesgradually ; it is composed in places of sandstones andconglom
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