various parts of Scotland. 425 



the nature or true place of these rocks. An accident common to 

 many species is not the characteristic of any. As well might gra- 

 nites and micaceous limestones form one species from their partici- 

 pation 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 por- 

 phyry. 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 accumu- 

 lation 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 acci- 

 dental features. Thus we shall have porphyritic traps and clay- 

 stones, or, if our grammatical ears are not offended by it, we may 

 have felspar porphyry, and hornstone porphyry. These are as- 

 sociations 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 



