AGE OF THE ARAPAHOE AND DENVER. 229 



fishes, birds, and a remarkable mammalian fauna. There are also mollusks 

 and fossil plants. 



Geological significance of the Ceratops fauna. The Vertebrate foSSils grOUped 1)V 



Professor Marsh in the Ceratops fauna have hitherto been referred to 

 by him as coming "from the Laramie of Wyoming," of Montana, i>r of 

 Colorado, and no doubl has been expressed by paleontologists of this 

 country concerning the reference of the strata containing these remains to 

 the Cretaceous rather than to the Eocene. The fauna is said to exhibit 

 pronounced Mesozoic affinities and remote connection with the earliest 

 Tertiary forms. In the closing discussion of evidence further reference 

 will be made to the basis for this opinion, but it is desired to show in this 

 place thai present knowledge does not permit the use of the Ceratops 

 fauna, extensive and remarkable as it is, in distinguishing the post-Laramie 

 from the Laramie proper. The cause of the inability to use thi> remark- 

 able fauna lies in the fact that the distribution of the species within the 

 series of formations in question is not satisfactorily known — precisely the 

 difficulty hitherto experienced with the fossil flora. A review of the facts 

 concerning the leading localities makes this clear. 



The Ceratops beds as a "horizon." Tile Strata ill wllicll tile < !< 'HI 1 1 I] )>]< la- alll] 



associated fossils occur have been grouped by Professor Marsh as the 

 "Ceratops beds," and frequently referred to by him as constituting "a 

 well-marked horizon." Although such a use of the term "horizon" may 

 be satisfactory to the vertebrate paleontologist, it is clear, on the grounds 

 already presented, that it. does not adequately express the facts of 

 stratigraphy. 



The Ceratops "horizon" in the Denver region embraces the Arapahoe 

 and Denver formations, and if the Laramie proper of other regions contains 

 the same fauna, the '•horizon" really embraces three stratigraphically 

 distinct formations. Aside from its inaccuracy, it seems to the writer 

 that this use of the term '-horizon" is quite unjustifiable, for it can not 

 but be misleading to those unacquainted with the regions involved. 



'The first Ceratops (C. montanus) was described by Professor Marsh in 

 December, 1888. 1 The locality and horizon in which the new fossil was 



/ ' Am. Jour. Sci., 3d series, Vol. XXXVI, 1888, p. 177. 



