21 



the author has decided, and on which the present 

 work has been drawn up. It will, on the con- 

 trary, be seen that the defects are displayed in 

 great detail, while the advantages are presented 

 in a very condensed form. To palliate that which 

 is faulty, or to conceal that which is defective, is 

 to deprive ourselves of the chance of amend- 

 ment 



The following enumeration comprises the 

 principal advantages to be obtained by a geolo- 

 gical classification. 



It is founded on the most extensive and im- 

 portant affinities of the objects to be arranged, 

 and thus resembles in its principles the clas- 

 sification of plants according to their natural 

 orders. 



While it teaches, as far as is admissible in 

 such a work, the history of rocks as constituents 

 of the earth, it combines with that, all that ap- 

 pears important of their history as mineral com- 

 pounds: nor does it exclude the most minute 

 subdivision of varieties, which it also separates 



