All those influences are important, for they can never be brought out on any map, and yet they are an intrinsic part of the land. Furthermore, they are a part of the poignant forces that teach the traveller wonderment and awe of the desert when he camps in the mighty company of its gigantic spaces; particularly if he catches a gently poised breath of the Moslem’s “Allah!” which is an indelible part of the mystic sadness it holds. If we look, now, at the map, and picture that the Sahara is, broadly speaking, a vast sheet of sand with a few island mountains, it will suffice in dealing generally with its boundaries of the past. It is my belief that the Sahara is increasing in size, and I think there are many conditions that go to prove it. Wherefore I ask you, in the first place, to conceive that the sand in the desert has steadily risen, with consequent result that the shores have become appreciably less. The belt that has been so engulfed all around the margin, or wherever the surface was shallow, may be taken to represent the regions that are to-day pre-Saharan, though, so far as I am aware, such pre-Saharan areas are seldom more than vaguely referred to, and have not been geographically defined. I will take, as an example, the southern area of the Sahara, because I have visited it more than once and know that region best. Not vastly distant from the shore there is the mountainland of Aïr, standing high above the surrounding country. Let us suppose that, before the Sahara commenced to fill up and change, this particular mountainland was not surrounded by sand, but was a part of a fertile foreland, and that the bushland of the Western Sudan, with its tropical fauna and vegetation and rainy season, either jutted out as a wedge or stretched right across Africa about the 20th degree of latitude, or 5 degrees farther north than obtains, with any solidity, at the present time.[5] If that was the case intimate problems that I have had to contend with would be logically explained. My primary work in the Sahara was that of a field naturalist, and the following extracts from Dr. Hartert’s paper in _Novitates Zoologicæ_, May 1921, regarding my first journey, have bearing on one of the problems that I wish to deal with: “The best zoogeographical boundary, apart from the oceans, has hitherto been the Sahara, a wide belt of poorly inhabited and unexplored country. As long as we knew very little about it, this was a very simple question—north of the Sahara palæarctic, south of it Ethiopian. This contention, however, was bound to be shaken to some extent when the Sahara (as it is marked on maps) became zoologically explored. Until the second decade of this century the Great Desert had only been touched by zoological collectors on some of its borders.