den has placed witli reservations below tlie Fort Union series, leaving 

 their final location for future discoveries. 



ISTo vertebrate remains having come under the author's notice from the 

 Placer Mountain and Canon City formations, no further notice can be 

 here taken of them beyond the statement that they are as Meek indi- 

 cates of Cretaceous age, not far removed from the horizon of the coals 

 of Weber E.iver, Utah. The presence of ammonites and baculites above 

 and below them has indicated such a conclusion to Leconte*, as it has 

 in the case of the Weber River beds to Dr. Hayden.t To near the same 

 horizon is perhaps to be referred the coal observed by Prof. Marsh| 

 on the south side of the Uinta Mountains in Utah, which were overlaid 

 by strata containing Osirea congesta. This may, indeed, be referred to a 

 still older period, as that oyster is characteristic of l^o. 3, according to 

 Meek and Hayden. The Placer Mountain and CaSon City groups are 

 nearer to I^o. 5, but the precise relation to it has not yet beendetermined. 

 I therefore proceed to the Fort Union group as No. vi. 



This extended deposit is stated by Hayden§ to extend from the Missouri 

 Valley to Colorado, passing under Tertiary beds by the way. That this is 

 the case has been confirmed by the researches conducted in the northern 

 and eastern portions of Colorado during the season of 1873 by the writer.|| 

 1 present comparative lists of the vertebrate species known from the 

 Platte and Missouri Valleys in the respective Territories : 



COLOKADO. DAKOTA. 



Gompsetnys victus, Compsemys victus, 



Adoctis lineolatus, Adocus lineolatus, 



Plastomenus punctulatus, Flastomenus punctulatus, 

 Plastomenus insignis^ * * 



Trionyx vagans, Trionyx vaganSj 



* * Ischyrosaurus antiquus, 



Plesiosaurus occiduus. 



* # 



* * 



Bottosaurus perrugosus, 



Polyonax mortuarius, 



Cionodon arctattis, 



Hadrosaurus occidentalism Hadrosaurus occidentalis. 



The identity and correspondence of the species indicate that these 

 remote localities contain the remains of the same fauna. Further, the 

 presence of the orders Sauropterygia and Dinosauria establishes conclu- 

 sively the Cretaceous and Mesozoic character of that fauna.* This refer- 

 ence was made by the writer in 1869, and was at that time opposed to the 

 views extant, both geological and paleontological. The following ex- 

 hibits the state of opinion on this point at that time: 



1856. Meek and Hayden, Proceedings Academy Philadelphia, p. 63, 

 referred them to the Tertiary. 



1856. Meek and Hayden, 1. c, p. 255 5 Lignite referred to the Miocene. 



1856. Meek and Hayden, 1. c, 113; referred to Lower Tertiary. 



1856. Leidy, 1. c, p. 312. Thespesius occidentalis, (Hadrosaurus ; ) re- 

 ferred to the Mammalia and regarded as perhaps Dinosaurian. 



*Report on the Geology of the Smoky Hill Pacific Eailroad Route, 1868, p. 66. 



tAnnual Report, 1870, p. 168. 



X See an interesting article by Prof. O. C. Marsh on the Geology of the Eastern Uintah 

 Mountains; Amer. Jour. Sci. Arts., March, 1871. 



§ Annual Report, Colorado, 1869, p. 89. 



ifSee Bulletin of the United States Geological Survey, 1874, p. 10. 



* Two species are provisionally referred to the Tertiary genus Plastomenus, but are too 

 fragmentary for final determination. 



