These mountains, which Idrisi calls the "cold mountains," extend to the north-west of Jirift and are "fertile, productive, and wooded." "It is a country where snow falls every year," and of which "the inhabitants are virtuous and innocent." There have been changes since Idrisi's time, both moral and physical, but here is a strong item of evidence in favour of the theory of the gradual desiccation which has enveloped Southern Baluchistan and dried up the water-springs of Makran. What Idrisi called the "Great Desert" is comprehensive. All the great central wastes of Persia, including the Kerman desert as well as the basin of the Helmund south of the hills, the frontier hills of the Sind border up to Multan, were a part of it, and they were inhabited by nomadic tribes of "thieves and brigands." Modern Seistan is a flat, unwholesome country, distributed geographically on either side of the Helmund between Persia and Afghanistan. It owes its place in history and its reputation for enormous productiveness to the fact that it is the great central basin of Afghanistan, where the Helmund and other Afghan rivers run to a finish in vast swamps, or lagoons. Surrounded by deserts, Seistan is never waterless, and there was, in days which can hardly be called ancient, a really fine system of irrigation, which fertilized a fairly large tract of now unproductive land on the Persian side of the river. The amount of land thus brought under cultivation was considerable, but not considerable enough to justify the historic reputation which Seistan has always enjoyed as the "Granary of Asia." This traditional wealth was no doubt exaggerated from the fact that the fertility of Seistan (like that of the Herat valley, which is after all but an insignificant item in Afghan territory) was in direct contrast to the vast expanse of profitless desert with which it was surrounded--a green oasis in the midst of an Asiatic wilderness. The Helmund has taken to itself many channels in the course of measurable time. Its ancient beds have been traced and mapped, and with them have been found evidences of closely-packed townships and villages, where the shifting waters and consequent encroachment of sand-waves leave no sign of life at present.