If I had had time and means, it would have been extremely interesting to explore up to its starting-point the great depression I had just crossed, a depression which perhaps comes down from the region of Merga in the heart of the Libyan Desert, where the natives agree in declaring that there exists a little lake surrounded by a palm plantation. The probable position of Merga is between the 25th and 26th degrees of longitude east and 18th and 19th degrees of latitude north. This oasis is situated on the direct route from Ennedi to Dongola, about 200 miles from the last water-point of Ennedi (Gourgouro). [Illustration: FRENCH SUDAN Map to illustrate the WORK OF THE MISSION TILHO in TIBESTI, BORKU, ERDI AND ENNEDI THE GEOGRAPHICAL JOURNAL, AUG 1920. _Modified Polyconic (1/M. International Map) Projection._ _Published by the Royal Geographical Society._ TIBESTI Tilho] =6. Exploration of Ennedi.= Having reached the well of Diona on 11 November 1914 in the morning, I was joined next day by the camel-corps section of Borkou and Ennedi, which brought me fresh supplies and were charged with the mission of getting into touch with the nomads of eastern and central Ennedi, who refused to acknowledge our authority and committed acts of brigandage on our lines of communication. A few patrols in the neighbourhood having made it clear that the rebels had decamped before us and taken refuge on the high plateaux, the camel corps under the command of Captain Châteauvieux climbed the heights of Erdébé, where they began an active pursuit of the rebels. At the same time I reconnoitred the water-point of Aga, 30 miles further east on the route from Erdi to Dar Four, a route followed at that period by a certain number of Senoussist emissaries on their way to exhort the Sultan Ali-Dinar to join in the Holy War! For it will be remembered that Turkey had just at that date entered into the war against us, and that the plan of the German general staff included a vast Musulman rising destined to drive the French and British out of their African possessions.