376 HISTORICAL GEOLOGY. 



through the Cretaceous, true, ordinary,, or typical mam- 

 mals first appear in the lowest Tertiary, and immediately 

 became the dominant class. 



Some Preliminary Kemarks. Before describing 

 the Tertiary mammals, there are some points requiring 

 notice : 



1. The suddenness of their appearance is very remark- 

 able. In the very lowest Tertiary, without warning and 

 without apparent progenitors, true mammals appear in 

 great numbers, in considerable diversity, and even of the 

 highest order Primates, or monkey tribe. Now, in Eu- 

 rope, where there is a decided break and a lost interval, 

 this is not so surprising ; but even in America, where the 

 Laramie passes without break into the Tertiary, the same 

 is true. At a certain level the great dinosaurs disappear, 

 and the mammals take their place. A new dynasty and a 

 new age in history commence. It is impossible to account 

 for this by natural causes, unless we admit times of rapid 

 progress. In addition to this, we must also admit that 

 the apparent sudden appearance in a particular place is 

 largely due to migration. 



2. We have said that they appeared in great numbers 

 and considerable diversity. All the great branches of the 

 Mammalian class were represented in the first fauna 

 herbivores, carnivores, and primates or monkeys. Yet 

 these were not so distinctly separated as now. They tvere 

 all generalized types. If we represent all the orders and 

 families of mammals as branches and sub-branches of one 

 main trunk, then, as we go backward in time, these be- 

 come less numerous and less widely separated. In the 

 earliest Eocene the branches are few and very near to- 

 gether. The carnivores are but slightly separated from 

 the herbivores in fact, they are both omnivores. The 

 monkeys, also, were not yet fairly separated as typical 

 monkeys. They are therefore called Prosimiae, or pro- 

 genitors of the true monkey. Manifestly, if these branches 



