As the people are dying out also, these changes cannot be accounted for on the score of huntsmen. It is, I maintain, the natural result of increasing sand and the drying up and dying out of vegetation. Giraffes and ostriches have departed from a land that can no longer nourish them, and lions have disappeared because the gazelle which they hunted have grown scarce, and open water-holes are a rarity. Eventually the wart-hog and guinea-fowl will vanish from the land for like reasons. Furthermore, Nature accepts no denial to her whims of devastation, wherever they rule, and, in the Sahara, the sweep of her scythe has taken, in its path, the mowing down of the very people of the land, who depart, like the creatures of the wild, when the struggle for existence becomes no longer possible. Hence, in Aïr alone, there are scores of stone-built villages deserted and in ruins, and steeped in pathos, no longer harbouring a single living soul. In those, and in other ways, we learn that decay is sure. The elusive problem is to gauge the duration of its reign, which can only be conjectured, since the history of the Sahara is unwritten. It may have set in a very long time ago, and be moving slowly, or it may have been active but a few centuries. That it has altered the aspect of the land is, to my mind, undoubted. Here is an instance of the kind that sets one thinking. South of Aïr, in country that is now desert, there is a well of astonishing age, named Melen, in a basin surrounded by low hills of bare, rough, stony nature. It is sunk through _solid rock_ to a depth of 70 feet, and is old beyond all calculation. One looks down its depth and speaks in a hushed voice, and the dark chamber booms back a whole volume of sound; a pebble is dropped to the bottom and the splash of it sounds like the lashing of surf on the sea-coast. The wall of the well is seared, in a remarkable way, with deep channels worn in the solid rock by the friction of bucket-ropes that have passed up and down the well—for who knows how long? It seems almost impossible that they have been worn in an era within historic times. The well offers a problem. There is no good grazing around it; no means that would, to-day, enable a band of men to camp there for a prolonged period while they laboured (with rock-drilling implements, of which there is no record) on the tremendous task of sinking the shaft through solid rock. Natives have no knowledge of how the work was accomplished. Therefore I try to set back the hands of Time and look over the land, imagining it as once covered with vegetation for herds of camels and goats, and with pools of water in the low hills. And, as a dreamer, I conjure up a picture of a past when, mayhap, a tribe of happy nomads camped in the hollow, in olden times, with everything in the neighbourhood that they required for themselves and their herds; and the old chief of the camp setting out to keep his slaves employed, at a time of plenty,