The only want of this region is water; and if the natural deficiency of this necessary fluid can be anyhow supplied, all parts of the plateau will bear crops, except those which form the actual Salt Desert.

In modern, and still more in ancient times, this fact has been clearly perceived, and an elaborate system of artifical irrigation, suitable to the peculiar circumstances of the country, has been very widely established.

The system of _kanats_, as they are called at the present day, aims at utilizing to the uttermost all the small streams and rills which descend towards the desert from the surrounding mountains, and at conveying as far as possible into the plain the spring water, which is the indispensable condition of cultivation in a country where--except for a few days in the spring and autumn--rain scarcely ever falls.

As the precious element would rapidly evaporate if exposed to the rays of the summer sun, the Iranian husbandman carries his conduit underground, laboriously tunnelling through the stiff argillaceous soil, at a depth of many feet below the surface.

The mode in which he proceeds is as follows.