We now enter the Desert of Erosion, a mass of mountainous highlands; of ridges, peaks, and _cols_, intersected and, as it were, gashed by ravines where roll the winter torrents and the rivers which the heats of summer dry up, and which, hollowing and gnawing into the stony soil, spread themselves over the valleys and awake a transitory vegetation. The erosive action of the waters is, then, the special characteristic of this part of the desert, which the Arabs call _Kifar_, or "the abandoned country." Most of the streams which water it have their sources in Mounts Aurès and Zibans, which form its northern boundary. They have excavated wide intermingling furrows, whose intervening spaces are occupied by gypseous plateaux. The formations of less resisting power, the marls, clays, and sands, have been washed away. [Illustration: THE SAHARA (DESERT OF EROSION).] The waters, whether proceeding from rain, or the melting of the snows on the loftiest peaks, are very pure at first, and roll in deep beds with vertical sides; when they reach the plains, their channels grow wider and shallower. In the wet season, the floods burst the banks, and overflowing, carry down immense quantities of rolled pebbles, which are distributed over an extensive area; in ordinary weather they are reduced to thin threads of silver, which, on arriving in the desert, vanish completely. You must excavate the soil to obtain a supply of water, and when found, it is brackish. Frequently the beds unite, forming basins of greater or less extent and depth, which fill themselves at the close of the winter floods, and a few of which preserve, even in the winter season, a certain quantity of water. Elsewhere, the soil is only humid, thanks to the abundance of salt, which retains the moisture. In such places numerous slimy marshes occur, where the traveller may not adventure without peril. But in general the surface is dry, cracked, cloven, and completely parched. The Desert of Erosion is not completely inhabited. At intervals you meet with a few squalid villages, and a multitude of camel's-skin tents are scattered like black spots over the yellow or grayish plains, on the borders of the _chotts_ or scanty water-courses. Herds of goats and flocks of sheep wander in the valleys, browsing on the rare short grass. Columns of smoke arise from the Arab bivouacs, and the women of the Sahara group themselves around the wells and springs to fill the water-bags with which they load their asses.