250 GEOLOGY OF THE DENVER BASIN. 



with a few known in the Fox Hills .Many of the fresh-water species are 

 also known to range upward into Wasatch or Fort Union Eocene beds. 

 A.s mentioned in discussing the section at Castle Gate, Utah, the gradation 

 in character of the invertebrate lamia from the Fox Hills to the Wasatch is 

 so gradual and the section apparently so complete as to cause Dr. C. A. 

 White to suggest that in this region sedimentation was continuous into 

 Eocene times. Bui this view is opposed by the evidence offered by verte- 

 brate paleontology and does not accord well with the facts of stratigraphy 

 that have been se1 forth. 



It is at least plain that until the distribution of the invertebrate fossils 

 through the various formations under consideration is much better known 

 than at present the evidence of vertebrate animals and fossil plants is more 

 useful than that <»f the Mollusca. Even the presence of brackish-water shells 

 docs not prove the strata containing them to be of true Laramie age, tor Mr. 

 Weed has found in the Livingston formation forms which, according to 

 Mr. Stanton, are identical with some from the Judith River beds. 



vertebrate fossils.. — As shown l>v Professor Marsh in another chapter, the 

 vertebrate fauna of the Laramie and the formations here termed the 

 pOSt-Laramie is a verj remarkable one, and the consensus of opinion 

 among paleontologists that this great fauna is strongly Mesozoic in its 

 affinities has determined the present reference of the Arapahoe and 

 Denver to the Cretaceous. As has been shown, it is only in this broad 

 way that this vertebrate fauna can now he used as evidence in the question 

 under discussion in this chapter, and it will lie well to examine the "rounds 

 upon which the positive opinion as to the geological significance of these 

 fossils rests. 



The leading elements of this fauna are the dinosaurs and the mam- 

 mals, both represented by many genera and species, nearly all of them 

 new. 'Idie mammals are considered by Professor Marsh as mainly allied 

 to Jurassic types, hut it is believed by Professors Cope and Osborn that 

 they are intimately related to the mammals of the Puerco. The latter is 



referred h\ Professor Marsh to the base of the Kocene (lower Wasatch), 

 while Professor Cope classes it with the Mesozoic. The wide i lilfereiices of 

 opinion thus brought out charly deprives these mammalian remains of much 

 ot their value in the present discussion. 



