KOMECLATUEE OF FORMATIONS. 43 



places as synonymes But in the majority of strata it will be necessary to 

 preserve the special names : thus those of Bear River, Bridger, White River, 

 and Loup Fork, applicable to beds having no exact equivalents in Europe, 

 cannot be set aside for older ones, but must themselves be applied to cor- 

 responding faunal horizons elsewhere, should any such be found in future. 

 And it will rarely happen that the minor subdivisions of such faunae will be 

 found to have an extent sufficient to warrant their having other than special 

 names. 



In the accompanying diagram the series of strata of Europe and North 

 America, as determined by their paleontology, are placed side by side for 

 the purpose of comparison. Complete parallelism can only be predicated 

 of divisions of the first order, separated by horizontal lines. Such relation 

 is indicated by exact opposition of the areas representing the epochs in 

 question. In giving the minor divisions of the European epochs I have 

 generally restricted myself to those of the epochs which have American 

 equivalents. Where there is no equivalent on one side or the other, the 

 vacancy is represented by a diagonal Hne. In employing names for epochs 

 and their divisions, I have adhered to the law of priority as far as my knowl- 

 edge of the literature allows.* I have given a few names to American for- 

 mations, but only in instances where such had not been previously given. 

 In such cases I have pieferred employing the name of some characteristic 

 genus of fossils, rather than one of local origin. 



COMPARISON WITH THE SCALE DERIVED FROM PALEOBOTANY. 



I now consider another kind of relation presented by the American 

 and European horizons. I allude to the florae, for my knowledge of which I 

 am necessarily dependent on the labors of others. I first exhibit the deter- 

 minations of the ages of the American formations, already discussed, made by 

 Mr. Lesquereux on the basis of the vegetable remains which they contain. 

 I place by the side of these my own determinations of the ages of the same 

 beds, as already related. The former are derived from the full memoir of 

 Mr. Lesquereux in the Annual Report of the United States Geological Sur- 



* In the European system I have been much aided by the writings of Woodward, Gervais, H6bert, 

 Pomel, Gaudry, etc., and by the atlas of Professor Renevier, of Lausanne. 



