IMAGINE a blue-green ribbon of water some 60 yards wide, then rough sandy dunes 10 or 20 feet high, and then beyond, the desert, burning yellow in the sun-here and there partly covered with scrub, but for the most part seeming quite bare; sometimes flat and stony, sometimes tossed and broken, sometimes in great drifts and wreaths of sand, just like snowdrifts, delicately ribbed by the wind-the whole stretching away for miles, scores of miles, not a moving form visible, till it is bounded on the horizon by a ridge of hills of the most ethereal pink under an intense blue sky.