CLASSIFICATION OF ROCKS. 71 



stone, and argillaceous schist, sometimes contain 

 fragments or conglomerates, and are therefore 

 partly of mechanical origin, so that there is a 

 fundamental error at the outset ; while in the Tran- 

 sition rocks, there are limestones, greenstones, and 

 hasalts, of a purely chemical nature ; so that this as- 

 serted distinction has no existence. Organic remains 

 are also rare in the Transition rocks ; so that the 

 character is further defective : whence it is plain that 

 there are no mineralogical characters, either single or 

 combined, by which they can be distinguished from 

 the primitive. Nor is there any geological boundary 

 by which they are separated from this. None has 

 ever been assigned ; while it is evident, that whatever 

 boundary may be assumed, it must be removed, as 

 often as an organic fossil or an imbedded fragment 

 shall occur in a rock, inferior to that last fixed on as its 

 lowest member. Some authors cause it to include the 

 primary conchiferous strata of limestone and schist, for 

 the evident purpose of excluding organic fossils from 

 the primary class ; while, with others, it means the 

 lowest secondary strata, or any thing else which they 

 do not chance to understand. And when a recent 

 writer on the Pyrenees says, that the transition rocks 

 alternate therewith primary micaceous schist, we can 

 only wonder what new meaning this word is now to 

 possess. Lastly, the absence of the transition rocks, 

 when the primitive and secondary are present, is con- 

 tradictory to the hypothesis. This class, therefore, as 

 a natural division, is a nonentity; since it is not always 

 present, does not form a transition, has no permanent 

 or certain character, and has no assignable boundary. 

 If there are two or more real divisions in the primary 

 class, under the views of revolutions formerly held 

 out, it is certain that we cannot yet discover them ; as* 



