SEQUEL TO SYSTEMATIC GEOLOGY. 531 



Sect. 4. Geological Synonymy, or Determination of Geological Equi- 

 valents. 



IT will easily be supposed that with so many different sources of names 

 as we have mentioned, the same stratum may be called by different 

 designations ; and thus a synonymy may be necessary for geology ; as 

 it was for botany in the time of Bauhin, when the same plants had 

 been spoken of by so many different appellations in different authors. 

 But in reality, the synonymy of geology is a still more important part 

 of the subject than the analogy of botany would lead us to suppose. 

 For in plants, the species are really fixed, and easily known when 

 seen ; and the ambiguity is only in the imperfect communication or 

 confused ideas of the observers. But in geology, the identity of a 

 stratum or formation in different places, though not an arbitrary, may 

 be a very doubtful matter, even to him who has seen and examined. 

 To assign its right character and place to a stratum in a new country, 

 is, in a great degree, to establish the whole geological history of the 

 country. To assume that the same names may rightly be applied to 

 the strata of different countries, is to take for granted, not indeed the 

 Wernerian dogma of universal formations, but a considerable degree 

 of generality and uniformity in the known formations. And how far 

 this generality and uniformity prevail, observation alone can teach. 

 The search for geological synonyms in different countries brings before 

 us two questions ; first, are there such synonyms ? and only in the 

 second place, and as far as they occur, what are they ? 



In fact, it is found that although formations which must be consi- 

 dered as geologically identical (because otherwise no classification is 

 possible,) do extend over large regions, and pass from country to 

 country, their identity includes certain modifications ; and the deter- 

 mination of the identity and of the modifications are inseparably 

 involved with each other, and almost necessarily entangled with theo- 

 retical considerations. And in two countries, in which AVC find this 

 modified coincidence, instead of saying that the strata are identical, 

 and that their designations are synonyms, we may, with mere proprie- 

 ty, consider them as two corresponding series ; of which the members 

 of the one may be treated as the Representatives or Equivalents of 

 the members of the other. 



This doctrine of Representatives or Equivalents supposes that the 

 geological phenomena in the two countries have been the results of 



