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



satisfactory method of attack that must serve until such 

 a study can be made, and that is to consider all of the 

 members of the so-called Dakota flora that occur at known 

 geologic horizons in other areas in one category, and those 

 that have not been recorded at other and known horizons 

 in a second category that must remain under suspicion 

 until their horizon has been determined. 



I have recently determined the collections of fossil 

 plants from the Cheyenne sandstone of southern Kansas 

 and from the "Woodbine formation of northeastern Texas 

 for the U. S. Geological Survey. The Cheyenne sand- 

 stone rests on red beds and is overlain by the Kiowa 

 marine beds. It is, therefore, referable to the Washita 

 division of Texes and presumably corresponds to a part 

 of the Mentor of central Kansas. The Woodbine forma- 

 tion lies between the Washita division and the Eagle Ford 

 formation — the latter the Coastal Plain equivalent of the 

 Benton. The Woodbine has commonly been correlated 

 with the Dakota. Both the Cheyenne sandstone and the 

 Woodbine formation contain floras that would be called 

 Dakota floras in the sense that the "Dakota flora " means 

 merely Upper Cretaceous flora. The two have not a sin- 

 gle species in common and such " Dakota' ' forms as occur 

 in the Cheyenne are all forms limited to Cheyenne and 

 so-called Dakota, associated with older species never 

 recorded from the Dakota, whereas most of the Woodbine 

 species are "Dakota" species that have been recorded 

 from very many localities in such formations as the 

 Bingen sand, the Tuscaloosa, the Raritan, Magothy and 

 Black Creek formations. 



The Cheyenne flora is no more closely allied to the 

 Woodbine flora than the latter is to that of the Montana 

 group. It is, therefore, no more proper to speak of 

 Dakota flora in connection with the Cheyenne, and pre- 

 sumably also in connection with the Mentor, than it would 

 be to call the Benton fauna a Kiowa fauna or vice versa. 



Any Cretaceous formation containing dicotyledonous 

 leaves and known or thought to be earlier than the Ben- 

 ton has usually been said to contain a Dakota flora and 

 this was apparently the only criterion employed in the 

 recent field work. That there is a Dakota flora that is not 

 Comanchean must be obvious to anyone who has followed 

 the study of the Atlantic Coastal Plain Cretaceous or con- 

 sulted the various correlations that have been published 



