The bugler at his side raised his bugle to his lips and blew. The dozen chasseurs d'Afrique and the ten native scouts who formed the advance guard stopped upon the signal. A couple of hundred yards behind them the two companies of the Foreign Legion came to a standstill. The convoy of baggage mules upon the right flank, the hospital equipment, the artillery section, the herd of oxen which was driven along in the rear, in a word, the whole expedition, halted in a wood of dwarf-oaks and junipers at three o'clock in the afternoon. The order was given to gather wood for the night's camp fires, and the companies were dismissed. Each soldier made his little bundle and fixed it upon his shoulders. Again the bugle rang out, sounding the "Fall in." And the tiny force marched out from the trees of the high plateaux into the open desert. It was extraordinary with what abruptness that transition was made. One minute the companies were treading upon turf under rustling leaves, the next they were descending a slope carpeted with halfa-grass, which stretched away to the horizon's rim, with hardly a bush to break its bare monotony. At the limit of vision, a great arc like a mirror of silver glittered out of the plain. "Water," said a tall, bearded soldier, who marched in the front rank of the first company. It was he who had stepped from the train at Bel-Abbès with a light dust-coat over his evening dress suit. He passed now as Fusilier Barbier, an ex-engineer of Lyons. "No," replied Sergeant Ohlsen, who marched at his side: "the crystals of a dry salt lake." In the autumn of last year Ohlsen--or, rather, to give him his right name, Tony Stretton--had marched upon an expedition from Mesheria to the Chott Tigri, and knew, therefore, the look of those tantalising salt lakes. That expedition, which had conducted a surrey for a road to the Figuig oasis, had brought him his promotion. "But we camp by the lake to-night," he added. "The wells of El-Guethifa are close." The companies went forward, and above that salt lake they saw the mirages begin to shimmer, citadels and hanging gardens, tall towers and waving woods and majestic galleons, topsail over topsail, floating upon summer seas. At the wells the sheikh of the district was waiting upon a mule. "I want fifty camels with their saddles and their drivers at five o'clock to-morrow morning," said Tavernay; and although as far as the eye could reach there was no moving thing upon that vast plain except the small group of Arabs and soldiers about the well, by five o'clock the camels were squatting upon the sand with their drivers beside them. The mules were sent back from El-Guethifa that morning, the baggage was packed upon the camels, and the little force, insufficient in numbers and supplies, went forward on its long and untoward march.