Having left Faya on September 4 we arrived on the 11th at the foot of Emi Koussi, 125 miles to the north, passing on our way by Korou Koranga, where we renewed our supply of water. The spot is one of the most picturesque I saw during this journey to Tibesti; it is a natural cistern hollowed by the action of the falling waters in the deep and narrow bed of the wadi Elleboe, a torrential river that comes down from Emi Koussi. The way to it lies through a defile more than a mile long, so narrow that two men cannot walk abreast. The water lies at the bottom of a grotto, dark in spite of being open to the sky, and whose walls wind in and out in such a way that not only the drying desert winds cannot get to it, but that even the sun’s rays only penetrate to it for a few minutes each day about noon, and only get down to the level of the water during May and July, when the sun reaches the local zenith. I had neither the time nor the means to measure the length and depth, the approach between precipitous walls being so difficult; but the supply of water is such that the cistern has never been dry so long as the guides can remember, however long may have been the drought during which the torrent has ceased to flow; the water stays clear, cool, and pleasant to the taste, without the slightest salty flavour. The cistern of Derso, on the contrary, at the foot of Emi Koussi, near the pasturage of Yono, is broad, spacious, and subject to the drying action of sun and winds; a score of yards deep, it is easy to get at; but its greenish water, stagnant and thick with organic matter, has to be filtered before it can be drunk without disgust, and a period of twelve or fifteen months’ drought is usually enough to dry it up altogether. _Ascent of Emi Koussi._—In all probability the rebels of the regions we had just come through had withdrawn towards their strongholds on the top of Emi Koussi. A light detachment was sent out to make sure that this was so, while the greater number of our camels were left to rest in the pasturage of Yono, where I had a little zeriba built for the storage of our baggage and provisions and the security of the men I left to guard them. On the morning of September 13 we betook ourselves to the ascent of the mountain by a track strewn with boulders, the gradient being fairly easy for the first five hours’ march, as far as the salt springs of Erra Shounga. From that point it stiffened, and grew very steep indeed between 6000 and 9000 feet. The last part of the ascent to the entrance of the pass that leads into the interior of the crater required the utmost effort on the part of our camels, unaccustomed as they were to the going in mountainous countries.