It contains no water in its
crystallization, but melts in a sufficient heat, without any aqueous
fusion. Therefore, this salt must have been in a fluid state of fusion,
immediately before its congelation and crystallization.
It would be endless to give examples of particular facts, so many are
the different natural appearances that occur, attended with a variety of
different circumstances.
There is one, however, which is peculiarly distinct, admits of
sufficiently accurate description, and contains circumstances from which
conclusions may be drawn with clearness. This is the ironstone, which
is commonly found among the argillaceous strata, attendant upon fossil
coal, both in Scotland and in England.
This stone is generally found among the bituminous schistus, or black
argillaceous strata, either in separate masses of various shapes and
sizes, or forming of itself strata which are more or less continuous in
their direction among the schistous or argillaceous beds.
This mineral contains, in general, from 40 to 50 _per cent._ of iron,
and it loses near one third of its weight in calcination.
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