20 



CENOZOIC MA3IM\L HOBIZONS 



The mammalian life of this region from New Mexico on the south 

 to Montana on the north is fiilly known from the beginning to the 

 close of the Eocene epoch, wliile it is imperfectly known during the 

 Miocene and Pliocene epochs. It shows four phases in its relations 

 to Europe. 



1. Throughout the lower Eocene epoch it is closely similar to the 

 far-distant life of western Europe. (See first and second faunal 

 phases, pp. 33, 35-36.) 



2. There follows a middle and upper Eocene interval of faunal sepa- 

 ration from Europe. (See third faunal phase, pp. 42-43.) 



3. Again there is a faimal reunion, near the beginning of the Ohgo- 

 cene epoch; then a divei^ence, less marked than before; then a 

 reunion in the middle ^Miocene, and another in the Pleistocene. But 

 from the Ohgocene onward westeru America, northern Asia, and 

 Europe, or Eurasia, fomi a single great zoologic province until 

 the late Pleistocene. (See fourth, fifth, and sixth faunal phases, 

 pp. 57-60, 76, S2.) 



4. Finally, the present epoch is one of faunal divergence or sepa- 

 ration. (See seventh faunal phase, p. 84.) 



THE PLAINS REGION. 



The Tertiaries of the Plains Region he east of the Rockies from 

 Montana southward. 



During the entire Eocene epoch the countiy stretching to the 

 Mississippi and eastward to the Appalachians and Atlantic coast is, 

 with a few exceptions,'^ a terra incognita so far as its terrestrial 

 manmialian life is concerned. Glimpses only of its marine or sea- 

 shore manmialian life are afforded in the Zeuglodon zone^ of Alabama 

 and Florida and in other httoral marine deposits. Wliile tliis vast 

 eastern region contains no known Eocene mammal-bearing deposits, 

 it was undoubtedly the scene of a very active continental^ mammalian 

 life from the time of the emergence of the central area toward the 

 close of the Cretaceous, or during and after Laramie time. Yet our 

 knowledge of the hfe of eastern North America during the entire 

 Eocene is only what we gain by inference from our knowledge of the 

 life of the Mountain Region from Montana on the north (47°) to New 

 Mexico on the south (36° latitude), a relatively circumscribed area. 



Our earhest knowledge of the maromahan life of the Great Plains 

 is that suddenly afforded on its extreme western fringe or border in 

 lower Ohgocene time, and it is indeed a revelation. Again, with the 



« For example. Marsh has reported from the supposed Oligocene of New Jersey two species of mam- 

 mals. Elotherium and Protcipirus { Tapirams^ lalidus. 



b Zeuglodon is an aberrant whale-like form which probably originated in the Eocene of Xorth Africa. 



c As pointed ont by Suess. Xorth America has been a continent since the close of the Cretaceous, and 

 its great land surfaces are older, more permanent, and more extensive than those of Europe. The 

 land surfaces of Africa, however, are far older than either. 



