CORRELATION OF THE CENOZOIC 205 



EOCENE 



Basal. — The very opening of the Eocene furnishes one of the most 

 brilliant examples of the possibilities of precise correlation through 

 vertebrate life. Changes occurring in the interior of the American 

 continent may be compared precisely with those along the northern 

 coasts of France and Belgium. In each case great forms of reptilian 

 life persist to the very close of the Cretaceous; the conditions of the 

 American "Laramie," "Hell Creek," or Ceratops beds are similar 

 to those of the Danian or Maestrichtian of Belgium; both mark the 

 abrupt termination of the Age of Reptiles; both are overlaid by beds 

 containing a number of very distinctive types of archaic mammals 

 mingled with those of distinctive reptiles (Champsosaurus) found 

 alike in the Puerco of Mexico, the Fort Union of Montana, the 

 Thanetian of northern France. Thus we believe the opening of the 

 Tertiary admits of close correlation in the Old and New Worlds. 

 The succeeding rich Puerco-Torrejon mammalian life of New Mexico, 

 so far as known, parallels that of the Thanetian (including the 

 Cernaysian) stage of northwestern Europe. It is all Paleocene, or 

 Basal Eocene. 



Lower. — The beginning of the Lower Eocene is clearly defined in 

 the Rocky Mountain region and with equal sharpness in northern 

 France and Belgium by the appearance of Coryphodon, and by the 

 opening of the second faunal phase with its advent of modernized life. 

 Our Lower and Upper Wasatch correspond respectively with the 

 Sparnacian and Ypresian stages of France. It is represented in deep 

 and fairly rich exposures in northern New Mexico and in western, 

 central, and northern Wyoming. 



The Wind River of central Wyoming together with the Lower 

 Huerfano near the Spanish Peaks of Colorado marks the upper life- 

 zone of Coryphodon and may prove to correspond closely with the 

 Ypresian of France. In the Rocky Mountains the Wind River is read- 

 ily distinguished by the survival of a number of characteristic Lower 

 Eocene types {Coryphodon, Phenacodus) and the fresh arrival of a 

 number of equally characteristic Middle Eocene types (uintatheres, 

 titanotheres) . It is consequently an ideal transition fauna. Unfor- 

 tunately the formations believed to be of corresponding age in France 

 are poor in mammal remains. 



