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A true and correct geological arrangement is, 

 in fact, at present unattainable ; as we are not yet 

 perfectly acquainted with the order and relations 

 of rocks in nature. Whatever modification of it 

 is adopted, must therefore be confessedly imper- 

 fect. But it is not less the foundation for a per- 

 fect one. It offers a basis always susceptible of 

 correction, and gradually increasing in correct- 

 ness ; every investigation of the characters of a 

 rock, necessarily adding something to the mass of 

 knowledge on which it is founded. By its very 

 imperfections it affords a stimulus to observers ; 

 not to rival each other in distinguishing the mi- 

 nute differences of specimens only, but in extend- 

 ing the bounds of geological science. 



In addition to the imperfections above stated, 

 it must also be admitted that it is logically imper- 

 fect, that it is not founded on one simple and con- 

 sistent principle. This is a defect, if it be really 

 considered as an important one, which is probably 

 irremediable. The larger divisions are, accord- 

 ing to the principle adopted, drawn from the 

 order and general relations to the structure of the 



