53 



vancing ; but the groups into which rocks are 

 associated, and the common relation which many 

 of them bear to the arrangement of nature, have 

 prevented the necessity of much refinement in 

 distinguishing the several substances. General 

 terms have thus continued to answer the pur- 

 poses of geological arrangement and description, 

 at least to a certain extent ; since it is still appa- 

 rent to those acquainted with the subject, that 

 occasional confusion, leading in many cases to 

 important errors, has followed from too lax a use 

 of these. 



But no reform having been attempted until 

 these defects had, in the progress of fresh infor- 

 mation, accumulated to a considerable extent, it 

 has become impossible to apply a complete re- 

 medy without an alteration so violent as to change 

 all the habits already acquired. It is still how- 

 ever easy, as in the case of mineral species, to 

 frame a new term on a mineralogical principle, 

 whenever ft rock essentially different from those 

 formerly known, is discovered; an example of 

 which is here afforded in the case of Hypersthene 



