wAui>.] DISCUSSION OF THE TABLE. 533 



are principally attributed, and that a thorough study of the living flora 

 in comparison with the Tertiary flora not only bears out this conclu- 

 sion to a remarkable dejfree, but renders it possible to trace many of 

 the lines of migration and to fix with some precision both the space 

 and the time relations of glacial phenomena. 



We may now briefly revert once more, and for the last time, to the 

 question of the age of the Laramie group, in so far as this is indicated 

 by the similarity of its flora to that of other formations. Tlius far I 

 have confined myself to the published flora of that group in order to 

 ascertain how the case stood at the close of the pi'olonged discus- 

 sion which has been outlined relative to its age, in which discussion 

 Mr. Lesquereux has had the last word in his recent great work on the 

 Cretaceous and Tertiary Floras of the West. But I should admit that 

 I was led to consider this side of the subject by the occurrence in my 

 own collections from both the northern and the southern districts — in 

 the Lower Yellowstone Valley and along the Upper Missouri, at Golden 

 and other points in Colorado, at Carbon, Black Buttes, and Point of 

 Eocks, Wyoming, and at other localities — of new forms, some of them 

 unique and remarkable, but some bearing a striking resemblance to, or 

 identical with, forms already figured from other localities whose strati- 

 graphical position is definitively settled. While some of this latter class 

 have a Miocene aspect, as does the Fort Union flora in general, there 

 are others embodying the characters that are usually associated with 

 the Cretaceous flora. As already remarked, it is too early for me to 

 discuss these forms fully or in detail, although some of the more re- 

 markable or representative ones are figured in the illustrations at the 

 close of the paper. At present I can merely call attention to some of 

 these forms of Cretaceous aspect, as showing that the more familiar 

 we become with this flora the more closely we find it linked with the 

 Cretaceous floras below it, and particularly with those of America. 



There seems some reason to believe that we now have in Fort Union 

 strata a somewhat modified representative of the hitherto exclusively 

 Cretaceous genus Gredneria, so long known from the upper Cretaceous 

 beds of Blankenburg, in the Harz Mountains, since found in other Euro- 

 pean strata of the same or earlier age, and now added by Heer to the 

 middle Cretaceous flora of Greenland. Gredneria is the original form 

 upon which have since been erected the additional genera of the group 

 Etfinf/shausoiia, Protophyllum, and AHpidiophiillum. These are all char- 

 acteristic Cretaceous genera, Credneria and Protophyllum being found 

 both in the Senonian and the Cenomanian, and Aspidiophyllum being 

 confined to the Dakota group. Our form (Plates LVII and LVIII) 

 diii'ers somewhat from all that have thus far been described, and may 

 be sufficiently divergent to warrant the establishment of a new genus, 

 or it may be necessary to refer it to some other genus, but its resem- 

 blance to Credneria is suflScient at least to make it a strongly Creta-. 

 ceous type, and should its relationship to that genus be finally settled 



