HELL CREEK BEDS, CERATOPS BEDS AND EQUIVALENTS 229 

 3. VERTEBRATE EVIDENCE. 



a Dinosaurs. 



Basing their conclusions upon identity of forms as well as on gen- 

 eral similarity, there seems to be substantial agreement among ver- 

 tebrate paleontologists in regarding the dinosaur-bearing "Hell 

 Creek beds" and "Ceratops beds" as being of the same age. 

 Throughout the other areas described in this paper wherever the 

 dinosaurs have been found sufficiently preserved to admit of identi- 

 fication, they have been shown to be identical with those from the 

 principal deposits above mentioned. It may, therefore, be taken 

 as also established by vertebrate paleontology that the beds under 

 discussion are of identical age throughout the field over which they 

 have been traced. It is very much to be regretted that the series 

 of monographs planned by the late Professor Marsh on the several 

 groups of dinosaurs are, with the exception of that on the Ceratopsia, 

 still unpublished. A summary of present knowledge concerning 

 their distribution would be very helpful at this time, but, so far as 

 known to the writer, there is no place in the United States where 

 they are known to occur in undoubted Laramie. 



Vertebrate paleontologists have been so long accustomed to re- 

 gard the presence of dinosaurs as prima facie evidence of Cretaceous 

 age, that doubtless a storm of protest will be raised at the position 

 here assigned them; yet it should need but a moment's reflection to 

 show that there is apparently no inherent structural or physiological 

 peculiarity which barred them from crossing the line — if there be 

 such — between Cretaceous and Tertiary time. To the naive state- 

 ment that the dinosaurs possess "decided Mesozoic affinities" there 

 cannot be the slightest objection, since, being without known descend- 

 ants, it is possible to compare them only with their ancestors, which 

 were of course Mesozoic. It has also been urged recently, in all 

 seriousness, that the time-honored custom of denominating the Cre- 

 taceous as the "Age of Reptiles" will be broken down if the dino- 

 saurs are permitted to pass into the Tertiary, yet even this objection 

 does not seem serious, especially as there are other undoubted Ter- 

 tiary as well as living reptiles. The Nestors of American vertebrate 

 paleontology have all, at one time or another, admitted the possibility 



