TRANSACTIONS OF SECTION E. 623 



After an enormous period of undisturbed deposition of sand in the sea, the 

 fourth stage was ushered in by a period of great continental convulsions. On the 

 line of the future Tanganyika a huge boss of rock was intruded into the throbbing 

 crust, and the surrounding region elevated to a considerable extent, followed by 

 the subsequent collapse of the body of the elevated area originating the great abyss 

 of Tanganyika. 



The fifth great stage was marked by the formation of a channel through the 

 western coast mountain, causing the draining of the great central sea, which 

 immediately became the inner drainage area of the Congo. 



The sixth stage then saw Tanganyika isolated as a lake by itself, from which 

 time dates the moulding of its present scenery, the formation of an outlet, the 

 freshening of its waters, and the lowering of its level, and finally the intermit- 

 tency of the lake's outflow was explained by the probable fact that the rainfall and 

 evaporation nearly balance each other in ordinary seasons. 



3. On the Royal Geographical Society's Map of Eastern Eqrtatorial Africa. 

 By E. G. Eavenstein, F.B.G.8. 



The map, the construction of which had been intrusted to Mr. Eavenstein by the 

 Coimcil of the Royal Geographical Society, was intended to embody, in a tangible 

 manner, all the information that had been collected up to the time of publication. 

 Large as had been the number of African explorers, much yet remained to be done 

 before our knowledge, even of the more accessible parts of Africa, could be looked 

 upon as satisfactory. Apart from the line of coast, -where the minute surveys of 

 Captain Wharton and others afforded an excellent base, there were but a few isolated 

 localities which had been determined in a trustworthy manner by astronomical obser- 

 vations. On the Upper Zambezi, Livingstone, Molir, and Serpa Pinto differed in their 

 results to a very serious extent. Between Zanzibar and Tanganyika the only point 

 satisfactorily determined was the capital of Unyanyembe (which Speke observed), 

 whilst the delineation of the lake depended upon Captain Oambier's determination 

 of Karema. Von der Decken's expedition had supplied trustworthy information as 

 regarded the position of Kilimanjaro and other points nearer the coast. In Southern 

 Abyssinia, M. d'Abbadie's network of triangles, supplemented as it had been recently 

 by Cecchi and Chiarini, afforded an excellent basis for mapping a wide stretch of 

 country. The exact determination of the course of the Upper Nile we owed to 

 Captain Watson, R.E., who was fortunate enough to observe a transit of ' Venus,' 

 whilst at Gondokoro, in 1872. It resulted from this observation that Khartum lay 

 eight miles to the east of the position assigned to it by Captain Bizemont, a change, 

 sanctioned by the careful surveys made between El Fashr, Khartum, and Dongola 

 by the English engineers working under Mr. Fowler. Good longitudes were few 

 and far between, but latitudes were fortunately very numerous. 



As to altitudes, the results were most discordant, and differences of 1,000 feet 

 in a total altitude of 5,000 were by no means rare. The establishment of permanent 

 studies by the French and German African Associations would no doubt render 

 future observations for height more trustworthy. For the present, he thought we 

 ■were safe in assigning to Tanganyika a height of 2,700 feet, whereas the Victoria 

 Nyanza lay probably at an elevation of 4,000 feet. 



After a rapid examination of the principal explorations which had yielded 

 materials for the map, the vast region stretching along the eastern margin of the 

 Victoria Nyanza right away to Southern Abyssinia and Harar was pointed out as 

 the vastest and most promising field of exploration in Eastern Africa. 



On Senegal, Gambia, and the Gold Coast. By Commander Y. L. 

 Cameron, E.N., G.B. 



SATURDA T, A UG UST 26. 

 The Section did not meet. 



