TT. Cross — Post-Laramie Deposits of Colorado. 39 



"These remains are not transitional between Mesozoic and 

 Tertiary forms, but their affinities are with the former beyond 

 a doubt ; thus indicating a great faunal break between the time 

 in the Cretaceous when they lived and the earliest known Ter- 

 tiary, or between the Ceratops horizon and the Coryphodon 

 beds, of the Eocene Wasatch. The lower division of the 

 Coryphodon beds, or lower Wasatch (Puerco), is clearly 

 Tertiary, and the great break is between this horizon and the 

 Ceratops beds of the Laramie." Concerning the abundant 

 faunas of the two horizons, "the more the two are compared 

 the stronger becomes the contrast between them. Instead of 

 placing them close together, as some geologists seem inclined 

 to do, it will be more profitable in future to search for the 

 great series of intervening strata containing the forms that 

 lead from one to the other." " Bearing in mind all that is 

 known to-day of the development and succession of vertebrate 

 life in America, from the early Silurian on to the present time, 

 it is safe to say that the faunal break as now known between 

 the Laramie and the lower Wasatch is far more profound than 

 would be the case if the entire Jurassic and the Cretaceous 

 below the Laramie were wanting."* 



Professor E. D. Copef in his " Synopsis of the Vertebrate 

 Fauna of the Puerco series " (1888) considers the Puerco 

 fauna as widely distinct from that of the Wasatch, and points 

 out that among 106 species of vertebrates known from the 

 Puerco not one is found either in the Wasatch or in the Lara- 

 mie ; that some important Mesozoic types end in the Puerco ; 

 that "two orders universally present in the Eocenes, the Peris- 

 sodactyla and the Rodentia, are wanting from the Puerco"; 

 and that many Puerco forms are plainly the ancestors of 

 Eocene types. Shortly before this publication Professor 

 Cope;}; had assigned the Puerco and Laramie to the " Post- 

 Cretaceous " as expressing their relationship better than to 

 class one with the Eocene and the other with the Cretaceous. 

 It is worthy of note that the Puerco was assigned to the 

 Eocene by Professor Cope§ as recently as 1.883. 



Professor Marsh refers the Puerco to the lower Wasatch = 



* Since the completion of this -article Prof. Marsh has announced the presence 

 of Ophidians and true Lacertiiians with the gigantic dinosaurs of the Ceratops 

 beds, ''in the Laramie of Wyoming." No serpents have hitherto been found in 

 America below the Eocene. (Notice of new reptiles from the Laramie Forma- 

 tion. This Journal, vol. xliii, p. 449, May, 1892.) 



+ Trans. Am. Phil. Soc, vol. xvi, pp. 298-361. 



\ The Relations of the Puerco and Laramie Deposits. Amer. Naturalist, vol. 

 ix, p. 985, 1885. The Mesozoic and Casnozoic Realms of the Interior of North 

 America. Ibid, vol. xxi, p. 445, 1887. 



§ Monographs of the Hayden Survey, III, Tertiary Vertebrata, Book I, p. 4, 

 1883. 



