96 EVOLUTION OF TO-DAY. 



extensive list. It is true that not all of these 

 animals are found at the very bottom of the Silu- 

 rian, but even in the oldest rocks the fauna is suffi- 

 ciently diverse ; and before the age is over, all of 

 the important classes of animals have made their 

 appearance without previous warning. This sudden 

 appearance of life is certainly unexpected. The 

 possible organic nature of the Eozoan in the older 

 rocks is no help toward solving the difficulty. 

 Should this prove to be a fossil, it only shows that it 

 was possible for fossils to be preserved during the 

 pre-Silurian times. Evolution must, of course, 

 suppose that it was during this period that the first 

 forms of life were developing into the condition 

 which we find with the beginning of the Silurian. 

 The question is even more forcibly asked, if the 

 Eozoan be a fossil, why we find no trace of this 

 early fauna ? 



The only possible explanation of this sudden ap- 

 pearance of life in the Silurian, is an appeal to the 

 incompleteness of the record. Vast periods of time 

 must have elapsed before the Silurian times, during 

 which the world was peopled with living things, 

 every trace of which must be supposed to have been 

 lost. There can be no doubt that there was an 

 enormous period of time between the solidifying of 

 the world and the beginning of the Silurian. But 

 whether the world was inhabited at this time it is 

 impossible to prove. That a long period elapsed 

 between the latest pre-Silurian rocks of any one 

 locality and the earliest Silurian, is also unques- 

 tioned. But how long this lost period might have 



