AGRICULTURE AND REVENUE 261

run low, and carry comparatively little water to the plains.
[t is just at this season that water is urgently required for
agricultural purposes, consequently whole rivers are at
this season diverted into the fields.
India and Ceylon are full of ancient and long disused
irrigation systems. In Ceylon at the present moment
there in a project for restoring the old tank system of
irrigation of centuries ago, the full extent of which has

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hardly yet been traced out. In parts of Persia, Baluchistan,
 and Afghanistan the water-supply derived from irrigation
 is the only supply available, and a system of
anderground tunnelling has been developed (called
“Kanat” in Persia, and “ Karéz” in Afghanistan) which
atilises sources lying deep below ground-level. The
practical engineering shown in laying out these underground
 canals is of a very high order. Makrian and
south-west Baluchistan are full of the remains of ancient