nt of Volcanic Rocks. 29 
neissy, mica-schist, limestone, gre acke, syenite, and por- 
How then, after this, ei F the pene author 2am 
© the term trachyte, basalt, and phonolite, to. rocks of a 
icular epoch, and vaguely unite all the rocks mineralogi- 
ate ‘tenbeal 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 ga of the same rocks, to name them qnologicaly by 
Po A 
sandstone, trachytes of the greensand, recent trachytes, 
so obvious that the determination of the mineral char- 
antes of a rock must precede any @ artamps 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 
er a geolo sification. In fact, such a classification 
is a Tabular D1 stony. of Rocks, or of the globe’ s surface, an 
requires a great eal of previous description and comparison 
of all these rocks. i to their mineral nature. It is 
also founded on hypothetical views, since it is a mere arpa 
esis, and perhaps a false one, more pa articulat 
to the eanietan strata, and, above all, the Bie ee 
GB ore 
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 aed on oryctognostical pupaiples. The 
character inferred by the name must always be true of the 
rock to which it has been applied ;_ Recitative ghee as 
to.age or origin are kept out of view ; ‘at the same time that 
this arrangement displays Seoetenons ‘rocks known in a clear, 
concise, and ready manner, for the purpose of any u erior 
classification upon geognostl tical or geological principles that 
—_ be preferred.*- 
“ees te er absurdity of making the pinay only mame a a rock indica- 
ie ts mineral nature, but its. geological connexions, is instantly seen, 
tin that this ecole were acted on, not in one or two, but in all 
