MINERALS

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broad. It fills a depression in the desert, protected partly
by outlying hills of the Aravalli system and partly by
high sand ridges, or dunes, from being filled up by windblown
 sand, and it is not more than a few feet deep in
its deepest part. No one knows what the origin of the
saline deposit in this or other Rajputana lakes may be.
There may be underlying beds of salt, or (and this
hypothesis is favoured by geologists) there may be
nothing more than those saline principles which exist
in all lakes which have no outlet except by evaporation.
Beyond India, in Afghanistan and Persia, there are huge
depressions in the general level of the plains, which are
almost invariably associated with widespread stretches of
sandy soil, and which contain thick saline deposits whenever
 the heat of the sun’s rays has dispersed the water
in which they were dissolved. These salt flats appear
white and shimmery in the heat haze, stretching over
miles of country, and are called  kavirs ” in Persia, “ kaps ”
in Makran, and “hamuns ” in Baluchistan. But the salt of
these wastes is not usually the salt of commerce. There
is, however, one such depression to the north of Herat
(north-west of Panjdeh), which is an apparently inexhaustible
 source of commercial salt to the Turkoman and
Afghan districts adjoining. It should be noted, however,
that even running water is usually brackish throughout
these districts.
In India, when land becomes water-logged from excessive
 irrigation or other causes, a saline efflorescence
(called Reh) frequently appears on the surface, and is
absolutely destructive to all vegetation, although the irrigating
 water is reckoned as “sweet.” The Rajputana
lake supply is sweet water, but the saline sediment is
pure salt, which crystallises on the surface of the black
lake mud to a thickness of 8 or 10 inches in the middle
of the lake. It is quite possible to cross the lake on the
surface of the salt in exceptional seasons. Magnificent
pink cubes of salt, of 1} inch sides, are obtainable from
the lake centre; but the salt taken out for purposes of
trade is usually taken from near the edges, where the pink