HELL CREEK BEDS, CERATOPS BEDS AND EQUIVALENTS 233 



was continuous. No more plausible theory occurs to the writer 

 than that they were suddenly removed by epidemic disease, so 

 many examples of which among recent animals have been given by 

 Professor Osborn.*^ 



b Mammals. 

 There is, in the present connection, neither opportunity, nor par- 

 ticular occasion, for going exhaustively into the bearing of the mam- 

 mals on the questions here involved, other than a general statement 

 as to their apparently complete distinctness from the mammals of 

 the Cretaceous, and argeement with those of undoubted Tertiary 

 age. When the mammals of the "Ceratops beds" were first mentioned 

 by Marsh he made the following statement*^ concerning them: 



All the mammals are of small size. They are mainly Mesozoic in 

 type, and more nearly related to the Jurassic forms below than to 

 those in the Tertiary above. . . . These remains are not transi- 

 tional 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 Tertiary, 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. 



In this connection he also makes the following vigorous statement: 



Bearing in mind all that is known today of the development and suc- 

 cession of vertebrate life in America, from 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 earlier Jurassic and Cretaceous below 

 the Laramie were wanting. 



On the other hand Prof. H. F. Osborn''" in his " Rise of the Mam- 

 maha, " published the same year as the above quotation from Marsh, 

 and based on similar material, makes the evolutionary break much 



** Am. Nat., vol. 40, 1906, pp. 829-837. 



" Am. Jour. Sci. (3), vol. 43, 1893, pp. 249-251. 



*" Studies from Biol. Lab. Col. Coll., Zool., vol. i, 1893. 



