Gress: Fossil Plants of the Dakota. 275 



To simplify and to make more certain the reference to the various 

 specimens a number has been attached to each. This reference num- 

 ber appears in parentheses in the citation of specimens under the 

 various species in the accompanying: list. 



Grateful acknowledgment is hereby made to the authorities at the 

 Carnegie Museum for the privileges and facilities afforded for carry- 

 ing on these studies, and to Dr. O. E. Jennings for his ever-ready 

 helpfulness and general supervision. 



Brief Historical Notes Relating to Studies on the Dakota 



Formation. 



During the past sixty years much has been written on the " Dakota 

 Formation," including its geological characteristics, age, relationship, 

 and content. 



No attempt will be mad^ here to give a complete summary of the 

 history of this very important formation, but a very brief outline of 

 the more important points in its history and development will be re- 

 viewed in order to recall its location and correlation with other for- 

 mations. The history of the " Dakota Formation " really begins with 

 the year 1853, when Prof. Meek and Dr. Hayden were sent by Pro- 

 fessor Hall of Albany on an expedition to the Bad Lands of Ne- 

 braska, which at that time included all of the upper Missouri country, 

 for the purpose of collecting Tertiary vertebrate remains. 



On this trip many Cretaceous remains were collected at Sage Creek, 

 Great Bend, and other places. Along the Missouri from Ft. Pierre to 

 Belleview, a trading post a short distance above the present site of 

 Omaha, much attention was given to the lithological character, order 

 of succession, and characteristic fossils of the subdivisions of the 

 Cretaceous series. (U. S. Geological Survey of the Territories, IX, 

 1876, p. 22.) 



An account of the fossils brought back by this expedition was pub- 

 lished in the Memoirs of the American Academy of Arts and Sciences, 

 Boston, Volume V, 1856. 



Five divisions of the Cretaceous period of this region were formed 

 from the notes and were published in the same Memoir, p. 405. 



In subsequently published^apers by Meek and Hayden these five 

 divisions were amplified. Finally in 1861 the following names were 



