HELL CREEK BEDS, CERATOPS BEDS AND EQUIVALENTS 23 1 



several epochs succeeding the Laramie it is not clear to the writer 

 why this belief that the dinosaurs, or, indeed, the whole vertebrate 

 fauna, surely indicate a Mcsozoic age should be so positively main- 

 tained as is done by the vertebrate paleontologists. 



If the dinosaurs of the Ceratops fauna did actually live in the Lara- 

 mie epoch of Colorado they survived a great orographic movement 

 and its accompanying climatic changes, and continued through the 

 Arapahoe and Denver epochs so little modified that Professor Marsh 

 has not detected any changes corresponding to the stratigraphic 

 time divisions. This is all the more remarkable since the fossil 

 plants show a great modification during this time, and it has been 

 commonly claimed that enormous and highly specialized vertebrate 

 animals are particularly sensitive to conditions of environments. 

 If the Laramie vertebrates were unaffected by the known dynamic 

 phenomena of the Colorado region in post-Laramie times, it may 

 well be asked what caused their extermination in the post Denver 

 interval, where as yet no evidence of orographic movements com- 

 parable with that of the pre-Arapahoe have been found. And if 

 their extinction was due in large measure to other causes than those 

 associated with dynamic phenomena, may that extinction not have 

 been deferred until the Eocene? 



These considerations seem to the writer ample ground for the 

 demand that the causes leading to the extinction of the Ceratops 

 fauna should be definitely connected with some orographic disturb- 

 ance at the close of the Denver epoch before their presence in the 

 Arapahoe and Denver beds can be admitted as full proof of the 

 Mesozoic age of these formations. 



That the ground above taken is logical and irrefutable is shown 

 by the occasional testimony of vertebrate paleontologists themselves. 

 Thus, Mr. Earl Douglass*" in a paper dealing with the dinosaur- and 

 mammal-bearing beds near Melville, Montana, says: 



If we could point to any time when dinosaurs ceased to be and the 

 higher orders of mammals took their places, then the matter would 

 be easy; but heretofore most of the Cretaceous dinosaurs — in fact 

 nearly all of them — have been supposed to come from the upper- 

 most Cretaceous — the Laramie — but the other fossils found in these 

 beds have not been of a character to settle the doubt concerning 

 the horizon. There is no direct proof that the dinosaurs died out 

 before the higher forms of mammals became numerous. Though 

 they have not yet, so far as I know, been found in the same beds, 



" Proc. Am. Phil. Soc, vol. 41, 1902, pp. 2 18, 219. 



