29 



" The occurrence of [fossils specified] at the Judith River localities would 

 certainly strongly favor the conclusion, not only that this Judith formation, 

 the age of which has so long been in doubt, is also Cretaceous, but that even 

 the higher fresh-water Lignite formation at Fort Clark and other Upper Mis- 

 souri localities may also be Upper Cretaceous instead of Lower Tertiary. 

 That the Judith River beds may be Cretaceous I am, in the light of all now 

 known of this region of the continent, rather inclined to believe. But it 

 would take very strong evidence to convince me that the. higher fresh-water 

 Lignite series of the Upper Missouri is more ancient than the Lower Eocene. 

 That they are not is certainly strongly indicated not only by the modern 

 affinities of their molluscan remains, but also by the state of preservation 

 of the latter." 



I presume it is now apparent that the presence of the orders Sauropte- 

 rygia and Dlnosauria establishes, conclusively, the Mesozoic and Cretaceous 

 character of this fauna. This reference was made by the writer in 1869, 

 and was, at that time, opposed to the views extant, both geological and pale- 

 ontological. The following list exhibits the state of opinion on this point at 

 that time and subsequently. 



1856. Meek and Hayden, Proceedings of the Academy, Philadelphia, p. 63 ; 



referred them to the Tertiary. 

 Meek and Hayden, /. c, p. 265 ; Lignite, referred to the Miocene. 

 Meek and Hayden, /. c, 113 ; referred to Lower Tertiary. 

 Leidy, I. c, p. 312 ; Thespesius oocidentalis (Hadrosaurus) ; referred to 



the Manimalia, and regarded as dinosaurian. 

 Leidy, I. c, p. 89 ; Ischyrosaurus referred to the Marnmalia as a 



sirenian. 

 1860. Hayden, Transactions of the American Philosophical Society, p. 123 ; 



repeats former conclusions; Leidy refers Thespesius more decidedly 



to the Sauria, and questions relations of Ischyrosaurus. 

 1868. Hayden, American Journal of Science and Arts, p. 204; Lignites 



regarded as Tertiary, from both vegetable and animal remains, 



from the Missouri and the Laramie Plains. 

 Leconte, Exploration of the Smoky Hill Railroad Route, p. 65 ; the 



Middle Colorado beds are "older than those of the Missouri or 



Great Lignite bed of Hayden, which are probably Miocene," &c. 



