I stayed a week in Khartoum, where I was the guest of the Civil Secretary, Feilden Pasha, and Dr. P. S. Crispin, Director of the Medical Service. It was an enchanting week that I spent in that pearl of the Sudan, which is already visited by many a tourist, so great was the consideration shown me by my hosts and by the high officials and officers of the capital. I left Khartoum on August 24, arrived in Cairo in the morning of the 28th, and on the 30th had the honour of being presented at Alexandria by the French Diplomatic Agent to His Excellency the British High Commissioner in Egypt, Sir Reginald Wingate. As there was no boat ready to start for France, I was able to satisfy my impatience to see an up-to-date fighting front by a visit to the British front lines opposite the Turkish trenches which at that time defended Gaza. Then, returning to Alexandria, I embarked for Malta. From there I reached Syracuse, and thence, by Messina, Naples, Rome, and Modane, I arrived on 1 October 1917 in Paris, and from there a few weeks later I joined the French front. =10. Conclusions.= _Geographical Results._—In the course of this lengthy statement I have set forth in their respective places the principal geographical results obtained during the last five years of my stay in Central Africa; but it will perhaps be convenient to group them in a separate paragraph. In the first place, the great geographical problem of ancient fluvial communication between the basins of the Chad and the Nile is definitely solved; the mountainous barrier encircles the basin of the Chad from the Toummo Mountains on the north to the Djebel Marra on the south-east, passing through the massif of Tibesti, the plateau of Jef-Jef, the tablelands of Erdi and Ennedi, the hills of Zagawa, and the mountains of western Dar Four. In the second place, the lowest altitudes of the Chad basin are found in the plains of the low-lying region situated to the north-east of Lake Chad, which we have designated as “the Lowlands of the Chad.” The lowest altitude, of 160 metres (about 520 feet), was found in the ancient lake of Kirri, at a distance of about 250 miles from Lake Chad.