the nature or true place of these rocks. An accident common to many species is not the characteristic of any. As well might granites and micaceous limestones form one species from their participation in a common ingredient. Thus we are told that Cruachan consists of porphyry, that the Ochil hills consist of porphyry, that the Calton hill consists of porphyry, and that Rona consists of porphyry. Yet these four rocks are essentially different, and separated from each other as widely in composition as they are in geological relations, bearing, in short, no resemblance except in the common and unessential circumstance of imbedded felspar. For, the hornstone, the claystone, the trap and the felspar, which constitute the bases of these several rocks, although often containing crystals of felspar, are yet perhaps as frequently destitute of that accidental substance. I am not an advocate for increasing words, and encumbering our language with unnecessary terms, but that confusion which arises from applying one term to many substances, is at least as faulty and a greater cause of error than the accumulation of an unweildy stock of synonymous ones. If we must retain the ill applied term of porphyry, let it at least be returned to its place among the adjectives, and used as the trivial name to those species, which, for the purpose of description, can only be truly characterized by their permanent composition, not by their accidental features. Thus we shall have porphyritic traps and claystones, or, if our grammatical ears are not offended by it, we may have felspar porphyry, and hornstone porphyry. These are associations of substantives at least as tolerable as that of a line of battle ship.
I trust it will not be considered beneath the dignity of the Society if I here take notice of the assistance which the arts may derive from some of these porphyries. The green specimens are capable
Vol. II.3 h
