_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.
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