184 CRITIQUES AND ADDRESSES. [ix. 



evidence which M. Barrande has accumulated, and have 

 admitted the doctrine of colonies. But the admission 

 of the doctrine of colonies implies the further ad- 

 mission that even identity of organic remains is no 

 proof of the . synchronism of the deposits which con- 

 tain them. 



4. The discussions touching the Eozoon, which com- 

 menced in 1864, have abundantly justified the fourth 

 proposition. In 1862, the oldest record of life was in 

 the Cambrian rocks ; but if the Eozoon be, as Principal 

 Dawson and Dr. Carpenter have shown so much reason 

 for believing, the remains of a living being, the discovery 

 of its true nature carried life back to a period which, as 

 Sir William Logan has observed, is as remote from that 

 during which the Cambrian rocks were deposited, as the 

 Cambrian epoch itself is from the tertiaries. In other 

 words, the ascertained duration of life upon the globe 

 was nearly doubled at a stroke. 



5. The significance of persistent types, and of the 

 small amount of change which has taken place even in 

 those forms which can be shown to have been modified, 

 becomes greater and greater in my eyes, the longer I 

 occupy myself with the biology of the past. 



Consider how long a time has elapsed since the Miocene 

 epoch. Yet, at that time, there is reason to believe that 

 every important group in every order of the Mammalia 

 was represented. Even the comparatively scanty Eocene 

 fauna yields examples of the orders Cheiroptera, Insec- 

 tivora, Rodentia, and Perissodactyla ; of Artiodactyla 

 under both the Ruminant and the Porcine modifications; 

 of Carnivora, Cetacea, and Marsupialia. 



Or, if we go back to the older half of the Mesozoic 

 epoch, how truly surprising it is to find every order of 

 the Reptilia, except the Opkidia, represented ; while 

 some groups, such as the Ornithoscelida and the Ptero- 



