376 THE ORIGIN OF THE OLDEST FOSSILS. 



represented in the Lower Cambrian. Their home was not the bottom 

 of the deep ocean, bnt the shores of a continent nnder water of consid- 

 erable 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 larger by many fold than its history since. kSo 

 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 tlie 

 evolution of the ancestral stems took place at the surface, and all the 

 conditions necessary for the rapid production of types were pre.sent 

 when tlie bottom fauna first became established. 



As we i)ass backward toward the Lower Cand)rian we tind closer and 

 closer agreement with the zoological conception of the character of 

 primitive life on the bottom. While we can not 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 physical conditions and in its most distinc- 

 tive pecnliarities — the abundance of types, and the slight amount of 

 dillerentiation among the representatives of these tyi)es — and we must 

 regard it as a decided and unmistakable ai>proximation to the begin- 

 ning of the modern fauna of the earth, as distinguislied fiom the more 

 iiiicient and simple fauna of the oiJen ocean. 



