VEKTEBRATA OF THE TERTIAEY. 



of Colorado, Kansas, and northward, and in the valleys of the Rocky- 

 Mountains. A probably continuous succession of lakes has existed from 



this period to the present time in ever-dimin- 

 ishing numbers. The most important of these 

 were in the Great Basin in Oregon, in Wash- 

 ington, and in Nebraska, and their deposits 

 enclose the remains of a fauna entirely dis- 

 tinct from that of the Loup Fork period and 

 of more modern character. They are known 

 as the Equus beds. This fauna was proba- 

 bly contemporaneous with that which roamed 

 f" ^ through the forests of the eastern portion of 

 B ^ the continent, whose remains are enclosed in 

 the deposits of the caves excavated from the 

 ancient limestones. 



A more detailed account of the forma- 

 tions is now given. Faunal lists are reserved 

 for the close of the volume. 



a ^■ 



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 ^ . 



3 o 

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^ 2 



THE PDERCO. 



5 S 



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This formation, having furnished nu- 

 merous Mammalian fossils, is known to be- 

 long to the Tertiary rather than the Post- 

 Cretaceous series. It is regarded by Dr. 

 lilndlich as a subdivision of the Wasatch, 

 but the characteristics of its fauna are so 

 marked as to constitute it a distinct horizon. 

 The most southern locality at which it 

 ^. has been observed, the one from which I 

 named it, and where its characters are dis- 

 tinctly displayed, is west of the Jemez and 

 si Nacimiento Mountains, in New Mexico, at the 

 sources of the Puerco River. At this place its outcrop is about 500 feet in 



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