NATURAL SELECTION, AND THE ANTIQUITY OF LIFE 237 



animals, they were gigantic compared with primitive pelagic ani- 

 mals. The species were few, but they represent a very wide range 

 of types. All these types have modern representatives, and most of 

 the modern types are represented in the Lower Cambrian. Their 

 home was not the bottom of the deep ocean, but the shores of a 

 continent under water of a considerable depth. 



The Cambrian fauna is usually regarded as a halfway station 

 in a series of animal forms which stretches backward into the 

 past for an immeasurable period, and it is even stated that the 

 history of life before the Cambrian is longer by many fold than 

 its history since. So far as this opinion rests on the diversity of 

 types in Cambrian times, it has no good basis ; for if the views 

 here advocated are correct, the evolution of the ancestral stems 

 took place at the surface, and all the conditions necessary for 

 the rapid production of types were present when the bottom 

 fauna first became established. 



As we pass backward toward the Lower Cambrian we find 

 closer and closer agreement with the zoological conception of the 

 character of primitive life on the bottom. While we cannot regard 

 the oldest fauna which has been discovered as the first which 

 existed on the bottom, we may feel confident that the first fauna 

 of the bottom resembled that of the Lower Cambrian in its physi- 

 cal conditions and in its most distinctive peculiarities, — the abun- 

 dance of types, and the slight amount of differentiation among the 

 representatives of these types, — and we must regard it as a decided 

 and unmistakable approximation to the beginning of the modern 

 fauna of the earth, as distinguished from the more ancient and 

 simple fauna of the open ocean. 



