Descending from the high ground, they continued their course between the sand-hills and a blue inlet of the lake to the south. Some way to the right they caught sight of a whole herd of elephants, ranged in regular array like an army of rational beings, slowly proceeding to the water. It had been supposed that Lake Chad is salt. This is not the case. The natron or soda, which is procured in the neighbourhood, is found alone in the ground. When an inundation reaches a basin filled with soda, the water of course becomes impregnated. The soda, indeed, has very little effect so long as the basin is deep, and does not begin to make itself felt till the water becomes shallow. Shortly afterwards, passing a grove of mimosa, two of the horsemen who had been in front came galloping back with loud cries. On approaching the spot they saw a large snake hanging in a threatening attitude from the branches of a tree. On seeing the strangers it tried to hide itself, but after several balls had struck it, it fell down, and its head was cut off. It measured eighteen feet seven inches in length, and five inches in diameter. They now joined themselves to a party of Arabs, by whom they hoped to be protected on their journey. The expedition was not without danger. One night they were aroused by a terrible screaming and crying from the women, and shouts of "Mount! mount!" Another band of freebooters had attacked the camels, and, having put to flight two or three men and killed a horseman, had driven off part of the herd. The robbers were pursued and overtaken, when they gave up their booty. The lamentations of the females for a man who had been slain sounded woefully through the remainder of the night. Two days afterwards the Arabs were in great commotion, in consequence of the most handsome among the female slaves, who composed part of the spoil that was to be taken to the vizier, having made her escape during the night. They were eagerly searching for her from dawn of day, but could not find her. At length they discovered her necklace and clothes, and the remains of her bones--evident proofs that she had fallen a prey to the wild beasts. As they advanced eastward the situation of the Arab robbers became daily more dangerous; nothing was thought of but to retrace their steps westward.