COPE.] PALEONTOLOGY CRETACEOUS PERIOD AGE. 433 



No vertebrate rem aiDS having come under the author's notice from the 

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

 here t^ken 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 River, 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 Professor Marsht 

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

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

 still oWer p-eriod, as that oyster is characteristic of No. 3, according to 

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

 nearer to No. 5, but the precise relation to it has not yet been deter- 

 mined. 1 therefore proceed to the Fort Union group as No. 6. 



Tlvis extended deposit is stated by Hayden§ to extend from the Mis- 

 souri 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.|i I present comparative lists of the vertebrate species known 

 from the Piatte and Missouri Valleys in the respective Territories : 



COLORADO. DAKOTA. 



Conipsemys victus. Compsemys victus. 



Adocus lineolatus. Adocus lineolatus. 



Plastomemis punctulatus. Plastomenus punctulatus. 

 Plastomenus insignis. * * 



Trionyx vagans. Trionyx vagans. 



* * Ischyrosaurus antiquus. 



* * Plesiosaurus occidnus. 

 Botiosaurus perriigosus. * * 

 Polyonax mortuarius. 

 Cionodon arctatus. 

 ? Hadrosaurus occidentalis. Sadrosaurus occidentaU&. 



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 

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

 to the views extant, both geological and paleontological. The following 

 exhibits 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, loc. cit, p. 255 ; Lignite referred to the Mio- 

 oene. 



* Report on the Geology of the Smoky Hill Pacific Railroad Route, 1868^ p. 66» 



t Annual Report, 1870, p. 168. 



t See au interesting article by Prof. O. C. Marsb on theQ^ology of the Eastern Uintah. 

 Mountains; Anier. Jour. Sci. Arts, March, 1671. 



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



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



if Two species are provisionally referred to the Terti^ry.genus Plastomenus, but are to*, 

 fragmentary for final determination. 



28 GS 



* * 



