33. But granting that, either in the way just pointed out, or in some other that is unknown, the salt and the water have been separated, some further action of heat seems requisite, before a compact, and highly indurated body, like rock-salt, could be produced. The mere precipitation of the salt, would, as Dr Hutton has observed, form only an assemblage of loose crystals at the bottom of the sea, without solidity or cohesion: and to convert such a mass into a firm and solid rock, would require the application of such heat as was able to reduce it into fusion. The consolidation of rock-salt, therefore, however its separation from the water is accounted for, cannot be explained but on the hypothesis of subterraneous heat. 34. Some other phenomena that have been observed in salt mines, come in support of the same conclusion. The salt rock of Cheshire, which lies in thick beds, interposed between strata of an argillaceous or marly stone, and is itself mixed with a considerable portion of the same earth, exhibits a very great peculiarity in its structure. Though it forms a mass extremely compact, the salt is found to be arranged in round masses of five or six feet in diameter, not truly spherical, but each compressed by those that surround it, so as to have the shape of an irregular polyhedron. These are formed of concentric coats, distinguishable from one another by their colour, that is, probably by the greater or less quantity of earth which they contain, so that the roof of the mine, as it exhibits a horizontal section of them, is divided into polygonal figures, each with a multitude of polygons within it, having altogether no inconsiderable resemblance to a _mosaic_ pavement. In the triangular spaces without the polygons, the salt is in coats parallel to the sides of the polygons. The circumstances which gave rise to this singular structure we should in vain endeavour to define; yet some general conclusions concerning them seem to be within our reach. It is clear that the whole mass of salt was fluid at once, and that the forces, whatever they were, which gave solidity to it, and produced the new arrangement of its particles, were all in action at the same time. The uniformity of the coated structure is a proof of this, and, above all, the compression of the polyhedra, which is always mutual, the flat side of one being turned to the flat side of another, and never an angle to an angle, nor an angle to a side. The coats formed as it were round so many different centres of attraction, is also an appearance quite inconsistent with the notion of deposition; both these, however, are compatible with the notion of solidity acquired by the refrigeration of a fluid, where the whole mass is acted on at the same time, and where no solvent remains to be disposed of after the induration of the rest.