94 GRADATION AMONG ANIMALS. 



Now, what does this fossil creation tell us ? It 

 says this : that, in the Silurian period, taken in 

 its most comprehensive sense, the first in which 

 organic life is found at all, there were the three 

 classes of Radiates, the three classes of Mollusks, 

 two of the classes of Articulates, and one class of 

 Vertebrates. In other words, at the dawn of life 

 on earth, the plan of the animal creation with its 

 four fundamental ideas was laid out, Radiates, 

 Mollusks, Articulates, and Vertebrates were pres- 

 ent at that first representation of life upon our 

 globe. If, then, all the primary types appeared 

 simultaneously, one cannot have grown out of 

 another, they could not be at once contempo- 

 raries and descendants of each other. 



The diagram on the opposite page represents 

 the geological periods in their regular succession, 

 and the approximate time at which all the types 

 and all the classes of the Animal Kingdom were 

 introduced ; for there is still some doubt as to the 

 exact period of the introduction of several of the 

 classes, though all geologists are agreed respect- 

 ing them, within certain limits, not very remote 

 from each other, according to geological esti- 

 mates of time. 



If such discussions were not inappropriate here 

 from their technical character, I think I could 

 show, upon combined geological and zoological 

 evidence, that the classes which are not present 



