51 



founded, as already remarked, on geological nor 

 mineralogical principles, but is an unfortunate 

 combination of both, which often leads to con- 

 fusion. If a thorough reform were attempted, it 

 would appeal- preferable to construct a nomencla- 

 ture on geological principles ; as the wide and 

 general relations of rocks are the chief objects in 

 view in their classification. But to render such 

 a system perfect, an accurate knowledge of these 

 relations is required ; without which the parts 

 could not be arranged ; while, on the other hand, 

 an accurate knowledge of the parts is requisite 

 for the arrangement of the superstructure. Under 

 this double difficulty the subject at present la- 

 bours, nor is there any immediate prospect of re- 

 moving it. It must not be concealed, at the same 

 time, that there is an important evil which would 

 result from the adoption of a nomenclature 

 founded purely on geological relations. Through- 

 out the whole system of nature the same sub- 

 stances are occasionally repeated in situations ge- 

 ologically far asunder ; a fact, of which limestone 

 presents a conspicuous example. Such a nomen- 

 clature would thus dissociate two rocks which 



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