The thickness of the beds in each salt deposit of course depends
entirely upon the area of the original sea or salt-lake, and the length
of time during which the evaporation went on. Sometimes we may get a
mere film of salt; sometimes a solid bed six hundred feet thick.
Perfectly pure rock-salt is colourless and transparent; but one doesn't
often find it pure. Alas for a degenerate world! even in its original
site, Nature herself has taken the trouble to adulterate it beforehand.
(If she hadn't done so, one may be perfectly sure that commercial
enterprise would have proved equal to the occasion in the long run.) But
the adulteration hasn't spoilt the beauty of the salt; on the contrary,
it serves, like rouge, to give a fine fresh colour where none existed.
When iron is the chief colouring matter, rock-salt assumes a beautiful
clear red tint; in other cases it is emerald green or pale blue. As a
rule, salt is prepared from it for table by a regular process; but it
has become a fad of late with a few people to put crystals of native
rock-salt on their tables; and they decidedly look very pretty, and have
a certain distinctive flavour of their own that is not unpleasant.
Our English salt supply is chiefly derived from the Cheshire and
Worcestershire salt-regions, which are of triassic age. Many of the
places at which the salt is mined have names ending in _wich_, such as
Northwich, Middlewich, Nantwich, Droitwich, Netherwich, and Shirleywich.
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