I hesitated some time before continuing my journey towards this region, whose very name was unknown till now; my water-barrels only gave me a reserve of some thirty gallons, and my men’s skin bottles were so corroded by the salts of sodium they had transported that they were empty after twenty-four or thirty-six hours’ march. My camels, thin, worn out, and more and more mangy, could not do more than 20 miles a day, and I only had at my disposal ten days’ supplies for my detachment, so that any error on my guide’s part might put me into a critical position. _Erdi._—In spite of everything I resolved to make the attempt, trusting in fortune to ensure its success. In two marches we succeeded in reaching the foot of the cliffs of Erdi-Dji, 750 feet high and about 2000 feet above the sea. We found there good grazing for the camels, and from that day onward we had abundant fodder at each successive stage, so that I was delivered from the dread of seeing my indispensable beasts of burden waste away from inanition. The water was no less abundant, and was found in natural cisterns hollowed out by waterfalls in the beds of dried-up torrents that came down from the plateau. Some of these cisterns contained nothing but sand; but it was enough to bore a hole 1 or 2 feet deep in the sand to obtain a sufficient store of water. From the top of the cliffs all that could be seen was an immense plateau, slightly undulating, and rising gradually towards the north- east. Beyond the line of the horizon some dozen miles away, there rose, as our guide told me, other cliffs; but all I could do was to take note of that information without being able to verify it. Continuing our route eastwards along the foot of the cliffs, we reached five days later the region of Erdi-Ma, decidedly higher than that of Erdi-Dji: the highest altitude I had the opportunity of measuring exceeded 3000 feet. Our bivouac was installed at the entrance of the gorges of Dourdouro, where very picturesque natural cisterns are to be found containing abundant quantities of water withdrawn by the positions of the enclosing rocks from the drying action of sun and wind. During the whole of the way thither we did not see a living soul, any more than in the neighbourhood of Dourdouro. My guide never having gone beyond that point, it was impossible to push my investigations further. Besides, I had now only four days’ supplies left, a fact which obliged me to change my direction and make for Wad Mourdi, on the northern border of Ennedi, where I was to receive fresh supplies. I had eventually to be satisfied with determining the position of this point and measuring a few heights while we were renewing our store of water before starting again after a day’s rest.