Descriptive Arrangement of Volcanic Rocks, 29 



gneiss, mica-schist, limestone, greywacke, syenite, and por- 

 phyry." How then, after this, could the same author con- 

 fine the term trachyte, basalt, and phonolite, to rocks of a 

 particular epoch, and vaguely unite all the rocks mineralogi- 

 caily identical with them, but bearing appearances of a later 

 date, under the undescriptive, undistinctive term " Lavas." 

 How much more simple, after such a confession of the dif- 

 ferent ages of the same rocks, to name them geologically by 

 means of epithets superadded to their primary mineraiogi- 

 cal designation, in the same manner as the other rocks are 

 treated. We should then have secondary trachytes, tertiary 

 trachytes; or, if it was preferred, trachytes of the new red 

 sandstone, trachytes of the greensand, recent trachytes, &-c. 

 It is so obvious that the determination of the mineral char- 

 acters of a rock must precede any attempt to find its place 

 in a geological system, since it is only by these characters 

 that it can be distinguished from the other rocks with which 

 it is associated, that it is difficult to believe any person would 

 dispute the propriety, not to say the necessity, ofamineralo- 

 gical nomenclature being made use of for the primary terms 

 of a geological classification. In fact, such a classification 

 is a Tabular History of Rocks, or of the globe's surface, and 

 requires a great deal of previous description and comparison 

 of all these rocks according to their mineral nature. It is 

 also founded on hypothetical views, since it is a mere hypoth- 

 esis, and perhaps a false one, more particularly with respect 

 to the elevated strata, and, above all, the unstratified rocks, 

 that superposition is any proof of a posterior origin. The 

 arrangement of rocks on such a basis must necessarily be 

 dubious, insecure, and often erroneous. Whereas no error 

 can be committed in a nomenclature which is merely de- 

 scriptive, and founded on oryctognostical principles. The 

 character inferred by the name must always be true of the 

 rock to which it has been applied ; all speculative ideas as 

 to age or origin are kept out of view ; at the same time that 

 this arrangement displays the various rocks known in a clear, 

 concise, and ready manner, for the purpose of any ulterior 

 classification upon geognostical or geological principles that 

 may be preferred.* 



* The utter absurdity of making the primary or only name of a rock indica- 

 tive, not of its mineral nature, but its geological connexions, is instantly seen, 

 by supposing that this principle were acted on, not in one or two, but in all 



