Ch.II.] TERTIARY STRATA OF SUCCESSIVE PERIODS. 17 



French naturalists brought to bear upon their geological re- 

 searches so much skill and proficiency in comparative anatomy 

 and conchology, as to place in a strong light the importance of 

 the study of organic remains, and the comparatively subordinate 

 interest attached to the mere investigation of the structure and 

 mineral ingredients of rocks. 



A variety of tertiary formations were soon afterwards found 

 in other parts of Europe, as in the south-east of England, in 

 Italy, Austria, and different parts of France, especially in the 

 basins of the Loire and Gironde, all strongly contrasted to 

 the secondary rocks. As in the latter class many different 

 divisions had been observed to preserve the same mineral cha- 

 racters and organic remains over wide areas, it was natural that 

 an attempt should first be made to trace the different subdivi- 

 sions of the Parisian tertiary strata throughout Europe, for 

 some of these were not inferior in thickness to several of the 

 secondary formations that had a wide range. 



But in this case the analogy, however probable, was not 

 found to hold good, and the error, though almost unavoidable, 

 retarded seriously the progress of geology. For as often as a 

 new tertiary' group was discovered, as that of Italy, for exam- 

 ple, an attempt was invariably made, in the first instance, to 

 discover in what characters it agreed with some one or more 

 subordinate .members of the Parisian type. Every fancied point 

 of correspondence was magnified into undue importance, and 

 such trifling circumstances, as the colour of a bed of sand 

 or clay, were dwelt upon as proofs of identification, while the 

 difference in the mineral character and organic contents of the 

 group from the whole Parisian series was slurred over and 

 thrown into the shade. 



By the influence of this illusion, the succession and chrono- 

 logical relations of different tertiary groups were kept out of 

 sight. The difficulty of clearly discerning these, arose from 

 the frequent isolation of the position of the tertiary forma- 

 tions before described, since, a proportion as the areas occupied 

 by them are limited, it is rare to discover a place where one 

 VOL. in. C 



