[Illustration: A DESERTED STONE-BUILT VILLAGE OF AÏR] If we ponder over the thought that the Sahara is increasing in sand, and size, is it not conceivable that this mountainland of Aïr is as an island that, because of its altitude, is left high and dry out in the open while the plains surrounding it have been gradually smitten as by a plague that has slowly driven back the line of fertility, while that which remains, as representative of a configuration of the past, is the rugged rock land that still offers a bold front to the advances of time and decay? I am confident that therein lies the truth—that formerly a wide pre-Saharan region of fertility once reached much farther north than at present; and, when it became flooded over with rising sand, and lost, Aïr still remained, and, behind the shelter of its rocks, retained a good deal of its old characteristics. All around the Sahara I believe that conditions of a similar nature exist. Wherefore the vast arid interior, made up chiefly of rock and sand, may, to-day, be likened to a pear that has rotted at the core, and that cannot be prevented from increasing the consuming advance of an unhealthy interior that grows outward, and ever larger in circle. Stern and drastic though they are, I am prepared to accept those theories because they are in keeping with the nature of the country. Moreover, they lead to the solution of problems that ever bring me back to the source that is the cause of every change in the land—which I read to be _decay_. To make clear this perpetual insinuation of decay, which is everywhere in the atmosphere of the Sahara to-day, I will endeavour to cite a few instances that have bearing on the subject. First, reverting to the topic of the tropical life in Aïr. In 1850-51 Barth stated that he saw giraffes and ostriches, yet in 1909 we find that Jean wrote that “Giraffes and ostriches _do not exist_ in Aïr.” Both those travellers, however, recorded lions in the region, but in 1922, though I hunted particularly for lion, because of those very records, I could find neither trace nor track of a single specimen. All that my diligent investigations revealed was that one had been killed at Aouderas in 1915, and another, the last, in 1918 by the Chief of Baguezan. I believe them to be extinct in Aïr to-day. To give an opening for the further continuance of this sequence of singular disappearance of wild life, I can state that, at the present time, wart-hog and guinea-fowl live in Aïr—and I have actual specimens to prove it—but I am tolerably sure that travellers who may follow in my footsteps will come to find that both have disappeared within the next half-century or so.