291 



are not transitional between the Mesozoic and Tertiary forms, but their 

 affinities are with the former beyond a doubt ; thus indicating a great 

 faunal break. * * * and the great break is between this horizon 

 [the Peureo] and the Cera tops beds of the Laramie. * * * It is safe 

 to say that the faunal break as now known between the Laramie and the 

 lower Wasatch [Puerco] is far more profound than would be the case if 

 the entire Jurassic and the Cretaceous below the Laramie were wanting. 



Cope (Ainer. Naturalist, xxvi, 1892, p. 762). quoting from Marsh the 

 words "the more the two [Laramie and Puerco] are compared the stronger 

 the contrast between", adds : 



It is true that no Ungulata have yet been found in the Laramie, while 

 they abound in the Puerco, but we cannot be sure that they will not yet be 

 found ; the probabilities are that they existed during the Laramie and 

 that it is due to accident that they have not been obtained. But the Multi- 

 tuberculata of the two faunas are much alike. 



Osborn (Bull. Amer. Mus. Nat. Hist, v., 1893, p. 311) writes: 



This Laramie fauna is widely separated from the Upper Jurassic, and 

 is more nearly parallel with the basal Eocene forms of the Puerco and the 

 Cernaysian of France. * * * These conclusions are directly the re- 

 verse of those expressed by Marsh in his three papers upon this fauna. 



Cross (Geology of the Denver Basin, p. 220) concludes that this differ- 

 ence of opinion deprives the mammalian remains of much of their value 

 in the present discussion. 



To the present writer Marsh's opinion seems to be erroneous. Geo- 

 logically, of course, the Jurassic mammals are much farther removed 

 from those of the Lance Creek beds than the latter are from those of the 

 Puerco, Torrejon, and Fort Union. The same remark may justly be made 

 regarding the stage of development attained by the Jurassic mammals. 

 Systematically considered, the case is different; and the solution of the 

 problem depends on the systematic relationships of the Jurassic mammals 

 to those of the Lance Creek beds and of the latter to the mammals of the 

 Puerco and Torrejon. If it shall result that all, or nearly all, of the Lance 

 Creek mammals belonged to the Marsupialia and the Monotremata, then 

 Marsh's opinion will be in great measure justified. If, on the other hand, 

 it shall be shown hereafter that a large number of the Lance Creek mam- 

 mals were placentals and the near-by ancestors of the Puerco and Torre- 

 jon faunas the break between the former and the latter will not be a pro- 

 found one; nevertheless more important than formerly supposed by Os- 

 born. 



