76 CLASSIFICATION OF ROCKS. 



interfere with the primary, though of the most recent 

 date and connexions. Nor do I see any other ex- 

 pedient, except that of making a single class out of 

 all the unstratified rocks ; while I think that Geolo- 

 gists are not yet ready for such innovations. 



This is the great obstacle to a truly natural clas- 

 sification ; some minor apparent blemishes, yet rather, 

 practical ones than aught else, are soon described: 

 Such are the repetitions of the same rocks in more 

 classes than one. Custom has tolerated this separa- 

 tion in the limestones and others, and justly enough, 

 as a question of time: so that, following it, I have 

 done the same as to serpentine, and as to the rocks 

 modified by heat, namely, the siliceous schists, cherts, 

 and jaspers. The recurrence of the very same rocks 

 in different classes of the " secondary" strata, and also 

 in the tertiary, even indeed in the alluvia, as in traver- 

 tino, are practical or mineralogical blemishes of the 

 same nature; but if the classification is to be geolo- 

 gical, and for the purposes of geological science, this 

 must be; while the mineralogist may make his own 

 distinctions; Geology merely entreating, that he do 

 not attempt to write about it on such a basis, and 

 requesting the philosopher in names and specimens 

 to confine his genius to his own drawers, the logic of 

 which, like his own, is not that of Nature. 



Though there may be no prospect therefore of pro- 

 ducing an unexceptionable classification, either natural 

 or artificial, especially under the double and often 

 contending claims of Mineralogy and Geology, I am 

 bound to make the attempt: while, really, the other 

 branches of Natural History must recollect that then- 

 own success has not been very splendid, and, that among 

 the natural sciences, this most recent of all is almost 



