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.

_First_, That, the septa have been formed by the uniform contraction
of the internal parts of the stone, the volume of the central parts
diminishing more than that of the circumference; by this means, the
separations of the stone diminish, in a progression from the center
towards the circumference.

_2d_, That there are only two ways in which the septa must have received
the spar or spatthose ore with which they are filled, more or less,
either, _first_ By insinuation into the cavity of the septa after these
were formed; or, _2dly_, By separation from the substance of the stone,
at the same time that the septa were forming.

[Note 9: Plate I.]

Were the first supposition true, appearances would be observable,
showing that the sparry substance had been admitted, either through the
porous structure of the stone, or through proper apertures communicating
from without. Now, if either one or other of these had been the case,
and that the stone had been consolidated from no other cause than
concretion from a dissolved state, that particular structure of the
stone, by means of which the spar had been admitted, must appear at
present upon an accurate examination.

This, however, is not the case, and we may rest the argument here. The
septa reach not the circumference; the surface of the stone is solid and
uniform in every part; and there is not any appearance of the spar in
the argillaceous bed around the stone.

It, therefore, necessarily follows, that the contraction of the
iron-stone, in order to form septa, and the filling of these cavities
with spar, had proceeded _pari passu_; and that this operation must have
been brought about by means of fusion, or by congelation from a state of
simple fluidity and expansion.

It is only further to be observed, that all the arguments which have
been already employed, concerning mineral concretions from a simply
fluid state, or that of fusion, here take place. I have septaria of this
kind, in which, besides pyrites, iron-ore, calcareous spar, and another
that is ferruginous and compound, there is contain