Our factitious glass undergoes the same alterations: it decomposes and perishes, as it were, in the air. At first, it assumes a variety of colours, then exfoliates, and by working it, we perceive brilliant scales fall off; but when its decomposition is more advanced, it crumbles between the fingers, and is reduced into a very white fine talky powder. Art has even imitated nature in the decomposition of glass and flint. "Est etiam certa methodus solius aquæ communis ope, silices & arenam in liquorem viscosum, eumdemque in sal viride convertendi, & hoc in aleum rubicundum, &c. Solius ignis & aqua ope, speciali experimento, durissimos quosque lapides in mucorem resolvo, qui distillan subtilem spiritum exhibet & oleum nullus laudibus prœdicabile[218:A]." These matters more particularly belong to metals, and when we come to them, shall be fully treated on, therefore we shall content ourselves here with adding, that the different strata which cover the terrestrial globe, being materials to be considered as actual vitrifications or analogous to glass, and possessing its most essential qualities; and as it is evident, that from the decomposition of glass and flint, which is every day made before our eyes, a genuine clay remains, it is not a precarious supposition to advance, that clays and sands have been formed by scoria, and vitrified drops of the terrestrial globe, especially when we join the proofs _a priori_, which we have given to evince the earth has been in a state of liquefaction caused by fire. FOOTNOTES: [198:A] Essay on the Natural History of the Earth, pages 40, 41, 42, &c. [199:A] See Varennii, Geograph. General, page 46. [205:A] See the Mem. of the Acad. 1716, page 14. [216:A] See the Voyages of Francis Piriard, vol. 1, page 108. [218:A] See Becher. Phys. subter. ARTICLE VIII. ON SHELLS, AND OTHER MARINE PRODUCTIONS FOUND IN THE INTERIOR PARTS OF THE EARTH.