The impression of flatness is an optical illusion. Were a region that is as rugged as, say, New England to be completely stripped of its cities, villages, and farmsteads, its forests, lakes, and streams, its trees and grass, I imagine that, despite the pronounced irregularity of its surface, it would appear to one traveling across it to be a dead flat plain. So it is with the Sahara. In reality it is not flat at all. It has its mountains, its valleys, and its plains. Topographically speaking, it is a region of the most varied surface and irregular relief, broken by lofty table-lands and deep depressions, massive buttes and fantastic crags, vast steppes covered with water-worn pebbles and loose stones, cañons winding between precipitous walls, seas of shifting yellow sand and oases green with forests of date-palms and other fruit-trees. Its surface is still further diversified by numerous and extensive mountain ranges, at least one of which, the Ahaggar, has an area greater than the Alps and several peaks higher than any in the United States east of the Rockies. Yet the children in our public schools are still taught that the Sahara is nothing but a waste of sand, flat as a school-room floor! From this it will be seen that the Sahara has the makings of much picturesque and interesting scenery if it were properly upholstered. Its deadly monotony is due to a lack of diversity in color rather than to a lack of diversity in surface. The mountains, the plateaus, the crags, and the cañons are all there, but there is nothing to bring them out, to emphasize their presence. Since there is in that vast spaciousness nothing with which to compare them, they appear insignificant, hardly noticeable. Another thing. We of more favored lands are accustomed to what might be described as vertical scenery—trees, crops, church-spires, houses, fences—whereas the scenery of the desert is wholly horizontal. This still further makes for monotony, so, instead of examining the physical features of the country, the eye becomes wearied and is always looking off toward the horizon. I trust that I have now made it amply clear that the popular conception of the Sahara as an expanse of sand—a conception which motion-pictures and novels of desert life, as well as the illustrations in the popular magazines, have done much to foster—is quite erroneous. There are broad stretches of sand, it is true, the most extensive being the Igidi of Mauretania, the Grand Erg Occidental to the south of Algeria, and the Grand Erg Oriental to the south of Tunisia; but the actual area of pure sand is relatively small, covering only about _one tenth_ of the Sahara’s surface.