I read the trail as the camels move along, particularly when sheets of sand are spread before me. No one has passed ahead; no print of camel foot or donkey hoof marks the surface anywhere. The neat little cloven-hoof prints of Gazelle are fairly numerous and the feet of Field-mice have drawn countless little daisies on the sand where they have fed through the night about tussocks of grass. Other footprints tell where a Short-Eared Hare has loped across the ground, and I see where a hungry Jackal has picked up the trail and hurried in pursuit. At a cluster of bush I find the up-turnings of a Porcupine that has been burrowing and tearing at a shrub-bottom to feed on its favourite food—the roots of the pale-limbed, big-leaved bush which the Tuaregs call _Tirza_. In a shallow, dried-up river-bed the camels are guided clear of a regular warren of holes scooped out in the night by a Ratel in search of dormant frogs buried in the sand a foot or two beneath the surface. Nearing camping time the caravan reaches a terrace margin and descends a rocky slope, where the camels have difficulty in picking their way. A strange, wild valley lies in the unexpected level below, and a dry river-bed in a deep ravine. It is a drear valley-side, and the caravan passes on into the ravine below. In a cliff I find a deep, dark cave, and strike a match to enter it. It proves to be an old den of Hyenas; their footprints are on the dusty sand and the floor is littered with the bones of camels and other animals. The roof of the cave is festooned with the honeycombs of wasps, but the hives are forsaken. By this time the journey of the day has drawn to a close, and we camp to rest and eat, and refresh both man and beast, while my skinning-table and knives are set ready for the work of the evening on specimens that, mayhap, shall add to the knowledge of the world. Altogether, forty-two different species and subspecies of animals were collected from the Sahara and twenty-two additional varieties from the Western Sudan, on its southern shores. In the Sahara the following mammals were collected[20]: