PART III. 



THE AGE OF THE LIGNITIC FORMATIONS AS DETERMINED BY 

 THE CHARACTERS OF THE FOSSIL PLANTS. 



I have to meet at the beginning an objection which, if not refuted, might 

 leave some doubt of the reliability of the conchisions which I have drawn 

 from the characters of our fossil plants with regard to the evidence they 

 afford upon the age of the formations from which they are derived. 



This objection bears upon the uncertainty of some of the determinations 

 of the plants which are described in this work, the references to which have, 

 in a few cases, been moditied, as may be seen by the synonymy presented 

 with the species. I am the more inclined to take up the subject here, since 

 this will afford me the opportunity of giving due credit to those who have 

 contributed to the value of this memoir by communication of materials for 

 examination, and also of acknowledging the assistance rendered by scientific 

 friends interested in the progress of American paleo-botany. 



The first specimens used for the preparation of the Fossil Flora of the 

 Lignitic of the Western Territories were sent to me as early as 18G7 by 

 Dr. John L. Leconte, who gave a short account of these plants in his report 

 (p. 39) and in a note (p. 50).* They had been mostly collected around the 

 base of the Raton Mountains near Trinidad, and in Colorado. Though the 

 specimens were few and more or less fragmentary, I could then, from those 

 which were determinable, refer the Marshall's coal to the Lower Eocene. 

 Soon after I received from Dr. F. V. Hayden a new lot of fossil leaves, some 

 from the Laramie Plains, most of the others from Marshall's and Golden, and, 

 after a short description of them in Dr. Hayden's Annual Report, 1869, 

 p. 195, I concluded that the relation of the six species of Rock Creek was 



* Notes on the Geology of the Survey for the Extenslou of the Union Pacific Railway, E. D., from 



the Smoky Hill Eiver, Kansas, to tho Rio Grande, by John L. LeConto, M. D. (1868.) 



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