I first took the direction of the salt-pits of Arouelli, situated 28 miles to the northwards, where I met a caravan that had just loaded up with 30 tons of salt for the Wadai markets. The salt-bed lies at the bottom of an absolutely bare sandy depression, covering some 25 acres. The bed of salt, which is only about 6 or 8 inches thick, is on the surface, and more or less mixed with sand. The water-bearing stratum lies at a depth of 5 or 6 feet, and the water is naturally very salt. The water, rising to the surface by capillarity, evaporates, forming the salt crust that the caravans carry away in pieces, and which the natives of the Wadai and the countries bordering on it consume without further preparation. If one may trust the information supplied by the Ounias, the salt crust forms again about three months after being taken away, so that the output of the Arouelli pits would amount to nearly 100,000 cubic metres of salt annually, an output sufficient to satisfy the culinary needs of more than ten million people, and worth on the spot, as prices were before the war, some fifteen million francs. From Arouelli I went eastwards to fix the position of the well of Tekro, where there is also a deposit of salt which is not worked, the admixture of sand being too great. The well of Tekro is particularly important, because it is situated at the extremity of the great caravan route joining the Mediterranean to the Soudan by the oases of Koufra and the well of Sarra. The water is abundant and fairly fresh, but the vegetation is reduced to a hundred clumps of siwak and a few tufts of grass of no value for the feeding of camels. _The Route towards Koufra._—Between Tekro and Koufra the distance to be covered is about 350 miles, about half of which had just been reconnoitred by Lieutenant Fouché, commanding the garrison of Ounianga. Marching in a general direction north-north-east he had first crossed a rocky zone of slight elevation, spending four hours in doing so; then for two days he traversed an immense sandy plain, bare of all vegetation, with here and there stretches of rock surface level with the ground; broken lines of rocky heights were visible in the distance to east and west. These heights went to join the plateau of Jef-Jef, in the direction of which he marched for twelve hours during the third day. On the fourth, he found himself in a vast plain from which the Djebel Habid, 50 miles away to the east, can be seen during the first few hours. The fifth day ranges of moving sand-dunes that served as landmarks for the guides were observed to the north-west, and at last, at nightfall on the sixth day, he reached the well of Sarra, lying in a hollow running from south-west to north-east and 30 metres deep.