10 



isli water shells, including oysters. I do not know the depth of this 

 bed, but folio '.A'ed it to the southward until it disappeared beneath the 

 Loess of the South Platte. The age of this formation is no doubt, in the 

 main, identical with that which underlies the fresh-water basins of Dakota 

 and Wyoming, according to Hayden, and concerning which difference 

 of opinion exists among paleontologists. Mr. Conrad, to whom I have 

 submitted a number of shells, pronounces them to be species of Cyrena. 



Believing, as I do, that the evidence derived from the vertebrate re- 

 mains requires the reference of the Bitter Creek Coal Series to the Cre- 

 taceous period,* and having pointed out on similar grounds that the hor- 

 izon of the Great Lignite from which vertebrate remains have been pro- 

 cured on the Missouri River is undoubtedly Mesozoic,t although usually 

 regarded as Tertiary, I suspect that the corresponding strata in Colo- 

 rado will be found to pertain to the same section of geologic tiine-l 



It is thus evident that the relations of these three formations are 

 similar to those observed by Hayden to obtain between the Lignite, 

 White River, and Loup Fork epochs, in the West generally, and they 

 are in all probability to be referred to as near to those horizons. Prof. 

 Marsh has already stated the existence of the White River Tertiary in 

 Colorado,§ but subsequently in describing the Elotlierium crassum ^nd. 

 other species,|| remarks that the formation " probably belongs to a differ- 

 ent horizon." 



In the Pliocene strata above described, mammalian remains are ex- 

 ceedingly abundant over limited areas, those of horses in an especial 

 manner. Those obtained are as follows : 



Species. 



Carnivora 4 



Perissodactyla ^ H 



Artiodactyla T 



Proboscidia 1 



Testudinata 1 



Total , 21 



The most important paleontological results are: (1) The discovery 

 tliat the camels of this period possessed a full series of upper incisor 

 teeth; (3) that the horses of the genus Frotohippus are, like those of 

 Eippotherium, three-toed ; (3) that a Mastodon of the M. ohioticus type 

 existed during the same period. 



* See Proceed. Acad. Nat. Sciences Pbila., 1872, p. 27<). 



t Extinct. Batiacliia and Eeptilia of North America, 1S69, pp. 40-98. 



t Since the above was written and set np, I have obtained abundant evidence of the 

 correctness of this induction. In examining a collection from this formation, made by 

 one of my assistants, I find a series of Mesozoic genera of vertebrates as follows : 

 Dinosanria, Cinodon arctatus, gen. et sp. nov. ; Polyonax mortuarins, gen. et sp. nov. ; 

 Agatliaimas milo, sp. nov.; Testuvinata, Compscmijs sp.; Trionyx is also represented, and 

 a genus of Crocodilia nearer to the cretaceous form Bottosai'ieus than any other, so far 

 as the remains are indicative. Cinodon is a herbivorous saurian, to be referred to the 

 HadrosauridcB. The maxillary teeth are rod-like, with a narrow enamel face on the 

 inner side, the remainder of the surface being like a rat-tail file. The teeth have no 

 stem, and the successional crowns occupy an excavation on the posterior or outer side 

 of the shaft. They push the functional teeth inwards and upwards, so that the grind- 

 ing surface exhibits at one time a transverse section of three teeth, viz : an outer young 

 crown, a middle worn crown, and an internal stump. Longitudinally, three teeth also 

 exhibit the relative stages of protrusion, so that every third cross row is identical in 

 character. Enamel smooth, with a medium keel, and entire margin. Various parts 

 of the skeleton indicate an animal of the size of a horse. 



\^ Amer. Jour. Sci. Arts, 1870, p. 292. 



li Loc. Cit., 1873, p. 486. 



