ree of heat, that is, somewhat more than boiling
water, it enters into the state of aqueous fusion, and it boils, in
emitting the water by means of which it had been crystallised in the
cold, and rendered fluid in that heated state. It is not possible to
crystallise this alkaline salt from a dissolved state, without the
combination of that quantity of water, nor to separate that water
without destroying its crystalline state.

But in this mineral specimen, we have a solid crystalline salt, with
a structure which, upon fracture, appears to be sparry and radiated,
something resembling that of zeolite. 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. Before
calcination it is of a grey colour, is not penetrable by water, and
takes a polish. In this state, therefore, it is perfectly solid; but
being calcined, it becomes red, porous, and tender.

The fact to be proved with regard to these iron-stones is this, That
they have acquired their solid state from fusion, and not in concreting
from any aqueous solution.

To abridge this disquisition, no argument is to be taken from contingent
circumstances, (which, however, are often found here as well as in the
case of marbles); such only are to be employed as are general to the
subject, and arise necessarily from the nature of the operation.

It will be proper to describe a species of these stones, which is
remarkably regular in its