I sometimes think it was no wonder the old Sphinx got to asking conundrums. Always looking toward the desert and its mysteries, how could he help it? The desert is just full of conundrums. For instance: Where is it that rains fall without reaching the earth? [Illustration: _From the painting by Elihu Vedder_ THE QUESTIONER OF THE SPHINX ] Where is it that there are lake beds without lakes, river beds without rivers, and rivers without mouths? Where do you see stretches of water that aren't there, and men and animals walking and trees growing--most of them upside down? Where are the roses of the land and the waves of great inland seas made of sand and where does the wind always blow the mountains away? Of course you would probably give the right answer at once--"the desert"--because you know I am talking about deserts. And the "water that isn't there," and the trees and people and things that are upside down--you probably know that's the mirage; and that the inland seas with their waves of sand are the dunes; that the rivers without mouths are those that, like the Tajunga in California, lose their waters in the sand. Most people who have gone to school know all these things. Most people also think of the desert as just a sea of sand and all tawny, like a lion's skin; but this is wrong. The Romans used to call the African desert "the panther's skin," because of the tawny stretches spotted with the dark palms of the oases, but the sands are not all tawny, and the desert isn't all covered with sand. If we could arrange to get on the back of any one of the great birds of the Sahara--say an eagle or his big cousin the vulture--and sail with him on his way to dinner, the scenery would unroll beneath us something like this: On the northern border the Atlas Mountains, with precipices of wild beauty and ranges of bare, pink rock outlined against the blue of the morning sky; then dune waves stretching for miles and miles with valleys between them, so wide that it takes the camels from breakfast time until noon to lumber their way across. The crests of some of these dune waves go spinning off in spray with every freshening breeze. Little dunes often dissolve away in the wind as the caravan moves toward them. GAUNT OUTLINES OF THE HUNGRY HILLS