THE ORIGIN OF THE OLDEST FOSSILS, ETC. 479 



ern representatives, and most of the modern types are repre- 

 sented in the lower Cambrian. Their home was not the bottom 

 of the deep ocean, but the shores of a continent under water of 

 considerable depth. 



The Cambrian fauna is usually regarded as a half-way station 

 in a series of animal forms which stretches backwards 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. 



So far as this opinion rests on the diversity of types in Cam- 

 brian 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 estab- 

 lished. 



As we pass backwards towards 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 

 physical conditions and in its most distinctive peculiarities ; the 

 abundance 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. 



W. K. Brooks. 



Professor of Zoology in the Johns Hopkins University. 



