OF EVOLUTION. 45 



been discovered in any indisputable Cretaceous 

 deposit, and I may at once confess my inability 

 to satisfactorily account for this non-appearance. 

 But I feel perfectly safe in prophesying that they 

 will yet be found, and were I as sure of many 

 other things generally considered positive as I am 

 of this one, I could remain satisfied. 



In the first stage of the Tertiary period, known 

 as the Eocene, we meet with the earliest of the 

 placental mammals, or those forms in which direct 

 union is established between the young and parent 

 during the process of development. From this 

 period, it might be said, dates the origin of our 

 modern fauna. It will be seen from the chart 

 before you that only about one-half of the exist- 

 ing orders of quadrupeds are represented in the 

 Eocene period ; these are the marsupials, insect- 

 ivores, rodents, whales, hoofed-animals, bats, 

 lemurs, and possibly even monkeys. In addition 

 to these there are a number of orders which 

 have no living representatives at the present 

 day. In the Miocene, or middle Tertiary period, 



