The making of the Algerian highways has been no light matter. They have frequently demanded much engineering skill. Their repair is a difficult and expensive business, the heavy winter rains and the fierce summer sun have a rapidly disintegrating effect on the friable materials available. Algeria is not only an exceedingly mountainous country, but its physical conditions are very peculiar, and, except by those who have explored them, not as a rule very fully understood. The common idea of a fertile belt, more or less hilly and of varying width, between the sea on the north and the Sahara on the south, is imperfect and incorrect. As a very rough generalization, subject to innumerable variations of mountain and valley and plain, Algeria may be said to consist of two parallel ranges of mountains running north-east and south-west. The northern range slopes very gradually to the sea, often in a series of plains, providing with its copious rainfall that fertile tract known as the Tell, once the granary of Rome, and now again developing a great export trade. The Tell itself contains numerous ranges of lesser hills, called Sahels. The southern range faces the desert, in the east, in the great rocky mass of the Aures, with steep cliffs; in the west less abruptly. Between the two ranges is contained a lofty plateau, of convex form, in the main barren and sandy, but covered here and there with scrub. In many of its features it imitates the true desert. It has its shallow depressions filled with brackish water; and its inhabitants dwell in rare oases where fresh water occurs. The mountains attain no great elevation, their summits seldom exceeding 6000 feet. This is a pity. A lofty range treasuring copious stores of eternal snow would perhaps have made of the high plateau a veritable garden; and its influence would have been felt far southwards into the Sahara. The direction of the mountain lines causes the Tell, the land of tilth and colonization, to be wide at the western end of the Colony, in the province of Oran, and narrow at the eastern end, in the province of Constantine.