Age of Mammals 



THE EOCENE OF EUROPE AND NORTH AMERICA 99 



Roclaj Mountains Belgium France 



3. Lower Eocene, = 3. Upper Landenian = 3. Sparnacian 



Wasatch 



2. Basal Eocene, = 2. Lower Landenian = 2. Upper Thanetian 



ToRREJON (Cernaysian) 



1. Basal Eocene, = 1. Lower Thanetian 



Fort Union, 



PUERCO 



Age of Reptiles 1. Upper Creta- = Danian, Msestrich- 

 ceous, Laramie tian 



First, it will be observed that the Upper Cretaceous Laramie of America 

 is broadly regarded as of age equivalent with the Danian or M^strichtian 

 of Europe, also that both are characterized by a rich reptilian fauna, mark- 

 ing the close of the Age of Reptiles. 



Lying at the base of the Eocene or dawn of the Age of Mammals in 

 America are the Fort Union or great lignitic formation of Wyoming and 

 IMontana, and the Puerco of New Mexico; the latter is partly a tuff for- 

 mation. 



These are both continental deposits which are regarded as of the same age 

 as those sea border, or fluvio-marine deposits in northern Europe, which 

 are placed in the Lower Thanetian stage. 



We thus enjoy a contemporaneous picture of mammalian life as it 

 existed along the northern coasts of France and Belgium and in the river 

 valleys, flood plains, and lake borders of the newly born Rocky Moun- 

 tain region of New Mexico and Montana. For it must be remembered 

 (p. 93) that this region too had not long previously been on the borders 

 of an inland sea. 



Seashore transition beds in Europe. — The very ancient Basal Eocene 

 formations of Europe are along the sea borders and are thus not favor- 

 able to the preservation of mammalian life; yet the rocks are full of interest 

 as serving to illustrate how an ancient encroaching seashore may record 

 both its own life and that of the land near by. 



An especially clear sequence of these transition deposits is that recently de- 

 scribed by Deperet ^ in northern France near Rheims. (1) Immediately overlying 

 the Cretaceous are the Sables blancs siliceux de Rilly, white seashore sands of variable 

 thickness containing many marine molluscs which are similar to those in the Sables 

 de Bracheux, another Basal Eocene formation. (2) The overlying Gravier marin 

 de Cernay, or seashore gravels of Cernay (erroneously called 'ConglomcraV de 

 Cernay by Lemoine), containing species of typical marine molluscs characteristic 

 of the Upper Thanetian (Pedunculus, Ostrea, Lucina), is also a marine or shore 

 formation, rich in the teeth of sharks. The remains of mammals represent those 

 carried into the borders of a shallow sea tlirougli river currents; thej'' are iden- 



' Dep6ret, Relations stratigraphiques des Fauncs dcs Cernay ct de Mcudon au Mont de 

 Bemi. Soc. Geol. France, Scr. 4, Vol. VI, 1906, pp. 442-443. 



