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 form. It is that found at Aberlady, in East
Lothian.
The form of these iron-stones is that of an oblate or much compressed
sphere, and the size from two or three inches diameter to more than
a foot. In the circular or horizontal section, they present the most
elegant septarium[9]; and, from the examination of this particular
structure, the following conclusions may be drawn.
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