A third important result has been to reveal the geographical form of important mountain masses like Tibesti and Ennedi, hitherto shown in a very imperfect fashion on the maps of Africa, and the existence of another important massif called that of Erdi, connecting the two above mentioned. Moreover, the information we received permits us to reveal to geographers the existence in the centre of the Lybian desert of yet another mountain mass, the Djebel El Aouinat, situated about 150 miles south-east of the oasis of Koufra, and of which the altitude probably exceeds 4000 feet. A fourth interesting result has been the precise determination of the difference of longitude Paris-Faya by direct hearing of the wireless time-signals of the Eiffel Tower. Numerous rectifications of the positions attributed to various important points have resulted, the most notable being that which throws more than 50 miles to the N.N.W. the positions attributed by Nachtigal to Bardaï, the peak of Toussidé, the valley of Zouar, etc. A fifth important result is furnished by the discovery in northern Borkou of the _Harlania Harlani_, which authorizes us to affirm the Upper Silurian age of all the sandstone sedimentary formations of Tibesti, Erdi, and Ennedi. A sixth point will also, no doubt, be remarked by geographers: from the peak of Toussidé that dominates the north-west of the Tibestian massif to the Djebel Marra overlooking the plains of south-western Dar Four, that is to say, for more than 800 miles in a straight line, numerous hypsometric determinations have been effected which modify—sometimes by several thousand feet—the altitudes of the chief summits of the mountain chain that separates the basin of the Chad from that of the Mediterranean: in Tibesti, Toussidé, 10,700 feet instead of 8200, Emi Koussi, 11,200 feet; in Ennedi, the plateau of Erdébé, 4300 feet; in Tama, the peak of Niéré, 4700 feet; in Dar Four, the peak of Dourboullé, 7200 feet, the Djebel Marra, 9800 feet instead of 6000. These figures are given merely as an indication subject to the rectifications that will follow the revision now proceeding of the summary calculations rapidly effected during my journey. Lastly, the establishment of the geographical liaison between the Niger, the Chad, and the Nile, by a chain of astronomical positions determined with very satisfactory exactitude, constitutes a seventh result, all the more interesting in that it will permit the drawing up of four sheets of the international map of the world, thanks to the 10,000 kilometres of surveys traced by my collaborators and myself during this long expedition.