282 STANTON 



rior Region as it is of those in the Mesaverde and Judith River. 

 These mollusks evidently lived in tidal waters connected somewhere 

 with the open ocean. 



With all the oscillations the total result of the late Cretaceous move- 

 ments was uplift^^ and this finally brought the whole Rocky Mountain 

 and Great Plains regions permanently above sea level before the 

 beginning of the Tertiary, for the nearest marine Eocene rocks now 

 known are in eastern Texas, the lower Mississippi Valley, and on the 

 Pacific Coast. Some areas in the Rocky Mountain region must have 

 been subject to erosion for long periods before the close of the Cre- 

 taceous. The hypothesis that erosion did not begin until the close of 

 the Laramie in the Denver region, for example, and that time must 

 be allowed between the Laramie and the Arapahoe for erosion to 

 cut down through the 15,000 or 20,000 feet of sediments to the granite 

 in that region is to my mind incredible and unnecessary. 



Age of the "Ceratops Beds." 



Evidence from the vertebrale fauna. — The vertebrate fauna of these 

 beds is large and greatly varied, including mammals, dinosaurs, 

 amphibians, rhynchocephalians, turtles, crocodiles, and fishes. As a 

 whole and individually it is very closely related to the Judith River 

 fauna, which is known to be Cretaceous and to lie beneath a thousand feet 

 or more of marine Cretaceous beds. On this relationship with the 

 Judith River fauna Brown^- says: 



The vertebrates are clearly of Mesozoic affinity. The dinosaurs here 

 represented in the post-Laramie are the culmination of a practically 

 uninterrupted line of highly organized vertebrates that have persisted 

 with little change since the Judith River period, some like Claosaiirus, 

 extending as far back as the Niobrara, and their relation to the earlier 

 Jurassic forms is well established. 



*' I owe to Mr. Bailey Willis the suggestion that the facts would be better 

 explained by an ebb tide of continental extent due to deepening of the ocean 

 basins rather than by continental uplift. The fact of importance to my 

 argument is the change in relative positions of land and sea, and whether 

 this is due to continental uplift or to oceanic depression the resultant retreat 

 of the sea from the interior of the continent is the same. 



"Bull. Am. Mas. Nat. Hist., Vol. XXIII, 1907, p. 845. 



" Williston, S. W. : The Laramie Cretaceous of Wyoming, Science, N. S., 

 Vol. XVI, 1902, pp. 952-953. 



