The example now under consideration, consolidated mineral salt, will serve to throw some light upon the subject; for, as it is to be shown, that this body of salt had been consolidated by perfect fusion, and not by means of aqueous solution, the consolidation of strata of indissoluble substances, by the operation of a melting heat, will meet with all that confirmation which the consistency of natural appearances can give.

The salt rock in Cheshire lies in strata of red marl.  It is horizontal in its direction.  I do not know its thickness, but it is dug thirty or forty feet deep.  The body of this rock is perfectly solid, and the salt, in many places, pure, colourless, and transparent, breaking with a sparry cubical structure.  But the greatest part is tinged by the admixture of the marl, and that in various degrees, from the slightest tinge of red, to the most perfect opacity.  Thus, the rock appears as if it had been a mass of fluid salt, in which had been floating a quantity of marly substance, not uniformly mixed, but every where separating and subsiding from the pure saline substance.

There is also to be observed a certain regularity in this separation of the tinging from the colourless substance, which, at a proper distance, gives to the perpendicular section of the rock a distinguishable figure in its structure.  When looking at this appearance near the bottom of the rock, it, at first, presented me with the figure of regular stratification; but, upon examining the whole mass of rock, I found, that it was only towards the bottom that this stratified appearance took place; and that, at the top of the rock, the most beautiful and regular figure was to be observed; but a figure the most opposite to that of stratification.  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.  But to understand this specimen, something must be premised with regard to the nature of fossil alkali.