E. W. Berry — Age of the Dakota Flora. 387 



Akt. XXV. — The Age of the Dakota Flora 1 ; by Edward 



W. Berey. 



Nothing is more profitless than controversies regarding 

 geological boundaries or the precise age of those fossil 

 floras or faunas that existed at or near horizons where 

 geologists have been pleased to consider that such boun- 

 daries should be drawn. There are certain conclusions, 

 however, in Twenhofel 's otherwise admirable paper on 

 the Cretaceous of Kansas which appeared in the April 

 number of this Journal that should not be allowed to pass 

 unchallenged lest it be thought that they have the support 

 of the fossil flora. These are that the Cheyenne-Kiowa- 

 Reeder series of southern Kansas and the Mentor-Dakota 

 series of central Kansas, and the extension of the Dakota 

 in Nebraska, are synchronous with the Washita division 

 of the Texas section and therefore Lower Cretaceous in 

 age, and that the boundary between Lower and Upper 

 Cretaceous, or between Comanchean and Cretaceous as 

 Twenhofel prefers to call them, falls in Kansas between 

 the Dakota and the Benton. 



Twenhofel recognizes that Comanchean is not the 

 equivalent of the Lower Cretaceous of the rest of the 

 world, and that these Kansas formations, as well as the 

 Washita division of Texas, are probably to be correlated 

 with the Cenomanian stage of Europe and are therefore 

 Upper Cretaceous according to European standards. 

 What he fails to recognize is the results that logically fol- 

 low from his conclusions when the Cretaceous of other 

 parts of the United States are considered. 



The flora of the Dakota group as elaborated by Lesque- 

 reux comprised a great many species of fossil plants from 

 Kansas and Nebraska and some from as far northeast as 

 Minnesota and as far west as Colorado. Many were 

 without definite localities and no particular attention was 

 paid at that time to their stratigraphic position. It has 

 become increasingly clear of late years that "Dakota 

 flora" was not a unit and had no precise stratigraphic 

 value. A study of new collections made from known 

 stratigraphic horizons would be the only means of clear- 

 ing up this problem. There is, however, another if less 



1 Published with the permission of the Director of the XL S. Geological 

 Survey. 



