CHAPTER XII. 
THE FOSSILS OF THE EOCENE FERIOD. 
PISCES. 
The remains of fishes are abundant in the Wahsatch formation in North¬ 
western New Mexico. The families and orders represented are few, and 
present striking differences from, as well as resemblances to, those of the 
Bridger formation. The predominant family in New Mexico is the Lejpidos- 
teidcB, or Bony Gars, which are also abundant in the Bridger beds; but, in 
the latter, they are associated with equally numerous Ainndce, and Silurid<E, 
of which no trace has been discovered in New Mexico. Further, the teeth 
of Sharks occur sparingly in the latter region in the same beds with the 
Gars, while, in the Bridger beds of Wyoming, this gi’oup of animals is 
entirely wanting. 
The remains of Le]^idosteid(E are found everywhere, and in place. The 
teeth of the sharks are always more or less worn or rolled, and are most 
common in a bed of coarse sandstone which lies near the middle of the 
series. This bed also contains the teeth of Mammals, e. g., Ilyracotherium, 
Phenacodus, &c., in a similarly worn condition. Fragments of oyster-shells 
also occur in the same neighborhood; those that I procured not being in 
place as were the teeth. As the Eocene lake is supposed to have been 
fresh, and as the Lepidostei are not marine fishes, it becomes questionable 
whether the Oysters and Sharks are not intrusive fossils, derived from the 
adjacent Cretaceous strata which formed the shore of the ancient lake. In 
support of this view, I may state that I obtained one species, the Galeo- 
cerdo pristodontus, Agassiz, from both Eocene and Cretaceous formations, the 
latter in an unworn condition. In opposition to it, I may add that the Mani- 
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