VI LETTER TO THE SECRETARY. 



which are now reached, but the evidence they represented was deemed 

 inconclusive. Prof. Lesquereux was, therefore, desired to take the field 

 under the direction of the Survey, to study the Fossil Flora of these beds at 

 all the more interesting localities, from New Mexico through Colorado into 

 Wyoming and Utah. Some results of his researches, conducted during two 

 seasons, have already been given to the public in the Annual Reports of the 

 Survey, where the many new species discovered were named and briefly 

 characterized. Such description of fossil remains of plants, often represented 

 by mere fragments, was found to be inadequate to the full exposition of the 

 subject which science demands. It became necessary, therefore, to figure 

 these fossil plants with great care, in order that their characters might be 

 fully appreciated, and to compare them closely with those already known 

 from the different geological formations of Europe. By such representation 

 and examination alone, could safe conclusions be drawn respecting their true 

 geological I'elations. 



The carefully drawn plates which illustrate the subject, prepared by 

 Prof Lesquereux himself, or under his immediate supervision, place the 

 characters of these remains in the clearest light. The greater portion of 

 the text of this volume, forming Part Second, is devoted to the determination, 

 description, and discussion of the several species. The First and the Third 

 parts treat mainly of the geological bearing of the fossil plants and animals 

 upon the main question of the age of the Lignitic formations of the West, 

 and represent the conclusions derived from the study of the remains here 

 figured and described in connection with consideration of the evidence 

 afforded by the fossil animals. 



The author states that his final conclusions do not differ materially from 

 those already advanced by myself, and he regards the evidence as conclusive 

 that the Lignitic Group is of Tertiary age. This result is gratifying, not only 

 as settling the question at issue, but as silencing criticism of the value and 

 reliability of the general work accomplished by tlie Survey under my direction. 



Apart from the technical aspects of the scientific problem here solved, 

 the Lignitic formations of the West have an economic importance that cannot 

 easily be overestimated. Their wide extent and the number and thickness 

 of the beds of coal distributed througli tliese strata confer a value not less 

 than that of the true Coal-Measures of the East, from the Mississippi to 



