These hypogene rocks, again, he divides into unstratified or _plutonic_, and altered stratified, or _metamorphic_; the latter term implying the hypothesis that the stratified rocks to which it is applied have been altered, by the effect of fire or otherwise, since they were deposited. That fossiliferous strata, in some cases at least, have undergone such a change, is demonstrable from facts[34\4]. [Note 34\4: _Elem. Geol._ p. 17.] The modern nomenclature of chemistry implies the oxygen theory of chemistry. Hence it has sometimes been objected to. Thus Davy, in speaking of the Lavoisierian nomenclature, makes the following remarks, which, however plausible they may sound, will be found to be utterly erroneous[35\4]. 'Simplicity and precision ought to be the characteristics of a scientific nomenclature: words should signify _things_, or the _analogies_ of things, and not _opinions_. . . . A substance in one age supposed to be simple, in another is proved to be compound, and _vice versâ_. A theoretical nomenclature is liable to continual alterations: _oxygenated muriatic acid_ is as improper a term as _dephlogisticated marine acid_. Every school believes itself to be in the right: and if every school assumes to itself the liberty of altering the names of chemical substances in consequence of _new ideas_ of their composition, there can be no permanency in the language of the science; it must always be confused and uncertain. Bodies which are _similar_ to each other should always be classed together; and there is a presumption that their composition is _analogous_. _Metals_, _earths_, _alkalis_, are appropriate names for the bodies they represent, and independent of all speculation: whereas _oxides_, _sulphurets_, and _muriates_ are terms founded upon opinions of the composition of bodies, some of which have been already found erroneous. {297} The least dangerous mode of giving a systematic form to a language seems to be to signify the analogies of substances by some common sign affixed to the beginning or the termination of the word. Thus as the metals have been distinguished by a termination in _um_, as _aurum_, so their calciform or oxidated state might have been denoted by a termination in _a_, as _aura_: and no progress, however great, in the science could render it necessary that such a mode of appellation should be changed.' [Note 35\4: _Elements of Chem. Phil._ p. 46.]