It was all composed of concentric circles; and these
appeared to be the section of a mass, composed altogether of concentric
spheres, like those beautiful systems of configuration which agates so
frequently present us with in miniature. In about eight or ten feet from
the top, the circles growing large, were blended together, and gradually
lost their regular appearance, until, at a greater depth, they again
appeared in resemblance of a stratification.
This regular arrangement of the floating marly substance in the body
of salt, which is that of the structure of a coated pebble, or that
of concentric spheres, is altogether inexplicable upon any other
supposition, than the perfect fluidity or fusion of the salt, and the
attractions and repulsions of the contained substances. It is in vain
to look, in the operations of solution and evaporation, for that which
nothing but perfect fluidity or fusion can explain.
This example of a mineral salt congealed from a melted state, may be
confirmed from another which I have from Dr Black, who suggested it to
me. It is an alkaline salt, found in a mineral state, and described in
the Philosophical Transactions, _anno_ 1771.
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