74 TIIE DEVONIAN AND CARBONIFEROUS. | bull. 80. 



cessive groups with those of Europe, yet when we como to more minute and critical 

 comparisons the difficulties increase rather than diminish. 



The relations of our divisions often appear to be in two directions, and it is im- 

 possible to account satisfactorily for the apparent divergence in the direction of 

 groups, as shown by the evidence afforded by the recognized species of European 

 authorities. 1 



This determination of (correlation with) the Ludlow was independent 



of his determination of the true representative of the Devonian system 



in America; for in another place he said : 



The Oriskany saudstone, however, marks an important horizon, since we now regard 

 it as commencing the Devonian period. 2 



Although fossils were used for the purpose of correlating formations 

 across geographic intervals, as fronTEngland to America, it was not by 

 paleontology pure and simple. It was an identification of strata by. 

 likeness of fossils irrespective of the question of paleontologic history. 

 The fossils were mere " medals of creation ; " those possessing the same 

 marks were supposed to belong to the same creation. The time had 

 not come for an examination of the relations of the various fossils to 

 each other. The law of paleontologic succession did not become a 

 factor of correlation till the idea of the evolution of species furnished 

 a rational basis of confidence in the naturalness of the observed order 

 of sequence of forms. The idea of evolution suggests the true biologic 

 system of correlation, in which the data of the classification are fossils, 

 and the distinctions made are into periods in the history of organisms, 

 the strata taking their relative position in the series according to the 

 period in this history which their contained fossil remains may indi- 

 cate. 



1 Foster and Wlritnej r , Rept. on Lake Superior, pt. 2, p. 314. s Ibid., p. 302. 



