70 CLASSIFICATION OF ROCKS. 



to each other, though not to the primitive elass. Thus 

 the mutual boundary is placed where the change of 

 order occurs ; or the reverse position of two approxi- 

 mate strata, indicates that the lowest is the last or up- 

 permost of the primitive, as the other is the first, or 

 lowermost of the secondary class. If this reverse po- 

 sition should not exist, the boundary is then deter- 

 mined by mineral characters ; a conglomerate or sand- 

 stone being also the lowest secondary rock, wherever the 

 series is complete: while, if that should be absent, 

 some stratum known to lie above the conglomerate, 

 determines the boundary in question. Such is a view 

 of this arrangement ; giving it all the advantages of 

 modern improvements. Its truth and value will be ex- 

 amined, after Mr. Werner's improvement has been 

 stated. 



In this, the division is into Primitive, Transition, 

 and Flcetz ; while Secondary may be substituted for 

 the last term. The transition class, which alone re- 

 quires notice, is supposed to be distinguished from the 

 primitive, by containing rocks of a nature partly me- 

 chanical and partly chemical ; and further, by the pre- 

 sence of organic remains : as, hypothetically, it has a 

 presumed difference of origin, with which we have at 

 present no concern, further, than as thus occupying an 

 intermediate place between the primitive and secondary, 

 it is said to have been formed at an intermediate 

 mysterious period. It ought to be natural, as it 

 is asserted to be so ; or if artificial, useful ; if it 

 is neither the one nor the other, it also involves 

 objections distinct from those which apply alike to 

 both the systems. 



It is not natural, mineralogically, even in the pri- 

 mitive class. Micaceous schist, quartz rock, lime- 



