Huns, Mongols and Turks, which poured out of Asia and by repercussion possibly loosed the subsequent migrations of the Germanic tribes, may have been actuated by problems of desiccation which decreased the habitability of their homelands and drove them to seek more hospitable territory elsewhere. The botanist Lavauden believes he has found evidences of quite recent desiccation in the Ahaggar region, at the very center of the Sahara; and the archeological excavations at the tomb of Tin Hinan in the same region would tend to suggest an aggravation of the desert conditions since the latter Middle Ages. In the great erg regions the epidermis of the desert dune is perfectly denuded sand, forming a white or golden carpet which registers the passage of an animal or the fantasies of the wind in clear but ephemeral prints.