208 GEOLOGY OF THE DENVER BASIN. 



or less clearly equivalents of either the Arapahoe or the Denver beds. Few 

 of them have heen examined as yet in any detail, but all furnish valuable 

 evidence bearing upon the question under discussion in this chapter, and this 

 evidence shows that the stratigraphic and lithologic facts observed in the 

 Denver Basin ran not be lightly regarded as of purely local importance. < 'n 

 tin- contrary, these formations are so widely distributed and agree so per- 

 fectly in the trend of the evidence they afford that the consideration as to 

 ill.' age of the formations of the Denver area plainly involves a logical and 

 consistent treatment of a most important period of Rocky Mountain his- 

 tory. The question as to the weight to be given the stratigraphic and 

 lithologic facts of the Denver area broadens at once to a discussion of the 

 dynamic history of the interval between Mesozoic and Cenozoic time, or 

 of the transition from one to the other. 



Questions of paleontology. — Since the identification of the Arapahoe and Den- 

 ver formations there have been many important discoveries of fossil 

 remains in the Laramie or in the younger group of local formations to 

 which the Denver and Arapahoe belong. The most remarkable of these 

 fossils are vertebrates, and in another chapter Professor Marsh briefly out- 

 lines the character of those most directly connected with the formations of 

 the Denver Basin. The interpretation of this new evidence in its bearing 

 upon the subject of this chapter necessitates the discussion of our present 

 knowledge concerning the occurrence and distribution of these fossils, and 

 also of the relation of paleontologic to other kinds of evidence, tor there 

 is not perfect harmony in the conclusions drawn from weighing the various 

 kinds of evidence. 



The fossil floras of the Laramie and post-Laramie formations have 

 been recently revised by Mr. Knowlton, and a concise summary of his 

 results will be found in a later chapter. The conclusions drawn from this 

 revision illustrate the self-evident fact, too often disregarded, that the occur- 

 rence and distribution of fossils must first be ascertained and accurately 

 recorded before they become of value in the classification of allied and 

 associated formations. 



In applying the data of paleontology to the present question it is nec- 

 essary to review both present knowledge of the fossils and the general 



