STONES, in natural history, are defined to be essentially compound fossils, not inflammable, nor soluble in water or oil, nor at all ductile; found in continued strata, or beds, of great extent; formed either of a congeries of small particles, in some degree resembling sand, and lodged in a smoother cementitious matter; or else of this cementitious matter, and the gritt or sand-like particles, running together into one smooth mass; or, finally, of granules cohering by contact, without any cementitious matter among them; or composed of crystal or spar, usually debased by earth, and often mixed with tale and other extraneous particles.
Of this class of fossils there are three orders; and under these, eight genera.
The first order comprehends all the coarse, harsh, and rough stones, of a lax texture, and composed of a visible gritt, resembling sand in form, and usually immersed in a cementitious matter, and of little natural brightness; scarce capable of any polish, and naturally mouldering away in form of powder from the tools of the workmen. The genera of this order are two, viz. the amnochista and pladuria; the former of which constitute our grey and rough slates; and the latter comprehends most of the stones used in building, particularly Portland stone.
The second order consists of stones moderately fine, of a more compact and even texture, scarce distinguishable construction, and affording no sand-like particles to the view: of some natural brightness, capable of a tolerable polish, and flying off from the tools of the workmen in form of small chips. Under this order are comprehended the sympezia and steganian.
The third order consists of stones of a very fine substance and elegant structure, naturally of a great brightness, and capable of an elegant polish; composed of granules of various shapes and sizes, but usually flattish, sometimes more, sometimes less distinct; and, in some species, running together into uniform masses, but never lodged in any cementitious substance. Of this order are the marbles, alabasters, porphyries, and granites.