Classifications of Rocks. 39 



another stratum which, from previous observations, is known 

 to lie above the conglomerate, is assumed at that point as the 

 lowest of the secondary class. Such is a view of the arrange- 

 ment into primitive and secondary ; giving it all the advantages 

 that have been derived from observations far more recent thnn 

 those of its original inventors. The limitation to its truth and 

 utility will be examined when the nature of Werner's attempted 

 improvement on it has been stated. 



In this arrangement the division is threefold, or into primi- 

 tive, transition, and floetz ; the last being a term for which 

 secondary may be substituted. The transition class, which 

 alone requires notice here, is supposed to be distinguished 

 from the primitive by its containing rocks, of which the nature 

 or texture is partly mechanical and partly chemical ; and 

 further, by the organic remains which are found in its mem- 

 bers. Hypothetically, it is also distinguished by a presumed 

 difference in origin ; a matter which cannot be examined here 

 for want of space, and which must be referred to an examina- 

 tion of geological theories, and to some possible future op- 

 portunity. 



Thus this class is, as the name expresses, a collection of 

 rocks, not only formed at a period intermediate between the 

 formation of the primitive and the secondary, but necessarily 

 occupying an intermediate place. It is proper to examine 

 how far this subdivision is either natural or useful, as it involves 

 a set of objections distinct from those which apply alike to 

 both the systems. 



It is not natural, for the following reasons. In the primi- 

 tive class, even of Werner, many rocks, such as micaceous 

 schist and quartz rock, sometimes contain fragments, and are 

 therefore partly of mechanical origin. Conglomerates also 

 occur in this class, as among the limestones and serpentines ; 

 and it cannot here be necessary to adduce examples of these 

 facts. If required, the reader may consult the Classification 

 of Rocks for them. In the transition class, again, limestones 

 and greenstones, or basalts, of a purely chemical nature, are 

 frequent ; and hence the distinction attempted to be founded 

 on these circumstances has no existence. Organic remains 

 are not necessarily found in the transition rocks, and thus far 



