78 THE MAMMALIA. 



mammals. By way of pointing out the position 

 and succession of the formations, we will here add 

 a tabular view of the more important strata ; first 

 those of the Old World, where Central Europe is, 

 of course, the part that has been longest and best 

 known, and then a comparison of the divisions of 

 the Tertiary of North America. At the same time 

 the names of the more important species are given 

 by the side of the different strata in which they are 

 found. All that lies above the Tertiary formations 

 is considered as Diluvium, the lowest strata of 

 which are frequently also called Quartary or Quar- 

 ternary. It need scarcely be stated that there is 

 no sharp boundary between the uppermost Tertiary 

 strata and the lower Diluvial, and that the separa- 

 tion of the upper Diluvial from the later Alluvium 

 is equally indefinite. Owing to this difficulty 

 in distinguishing the different formations, most 

 palaeontologists prefer speaking merely of a lower or 

 an upper stratum of the Tertiary, in place of sub- 

 dividing it into Lower, Middle, and Upper Tertiary, 

 Miocene or Pliocene. The following arrangement is 

 partly taken from a tabular view given by Gaudry ; l 

 in the case of America we have followed Marsh. 



1 Gaudry, Considerations sur Us Mammifdres qui out v6cu en 

 Europe a la fin de V&poqiie, miocdne. Paris, 1873. 



