212 THE CHAIN OF LIFE. 



but there are others belonging to quadrupeds yet unknown, 

 and there are also tracks of tortoises, crocodiles, and lizards, 

 and of a large wading bird. Such a bed, perhaps deposited on 

 the margin of a salt lake, resorted to as a " lick " by herbivorous 

 animals, and by the carnivorous species which preyed on them, 

 is well fitted, by the thronging life which it indicates, to teach 

 how little we can know of the actual number and variety of 

 the old inhabitants of the earth. 



In England, Eocene beds of the age of those of Paris, occupy 

 the valley of the Thames and the Isle of Wight and neighbour- 

 ing parts ot Hants. They have afforded mammalian fossils 

 similar to those of Paris, though less abundantly, but they are 

 rich in remains of marine animals and of land plants. 



Instead of describing the well-known animals of the French 

 and English Tertiaries, from these Eocene deposits upwards, 

 I shall shortly sketch the succession in America, as worked 

 out by Marsh and Cope, with the aid of the admirable summary 

 given by Gp.udry of the present state of knowledge with refer- 

 ence to the sequence of mammalian life from its appearance 

 in the Early Eocene up to the present time.' 



Eocene mammals, especially those gigantic whale-like 

 creatures called Zeuglodon (Fig. i8o), have been found in 

 Eastern North America, but the most remarkable discoveries 

 have been made in the Western Territories, where vast numbers 

 of bones are imbedded in certain ancient and wide-spread 

 lacustrine beds. It may be well to premise here that though 

 the division into Eocene, Miocene, and Pliocene is recognised 

 in America as well as in Europe, the limits of these groups 

 may not precisely correspond with those in the Old World. 

 Still we have this certain point of departure, that the Eocene 

 begins where the peculiar animals of the Cretaceous end, and 

 that the drying up of the later Cretaceous sea and the esta- 

 blishment of tlie Eocene land were probably nearly con- 

 temporaneous in both continents. It is true, however, in 

 ^ Les Enchainements du Monde Animah 



