go THE LIVING WORLD. 



(Fig. 9) represents the ages in the order of their 

 occurrence. In the subsequent pages the ages will 

 be referred to by the names given in the left hand 

 column in the figure, and for convenience of the 

 reader who may not be familiar with them, a num- 

 ber will be placed after the name of the age which 

 will indicate its relative order. Thus Archean (i) in- 

 dicates that the Archean age was the first of the 

 geological ages. 



The following brief description of the life of the 

 different ages will serve as an introduction to their 

 more careful study : 



PALEOZOIC. 



The Archean (i) is characterized by having no 

 traces of life. This does not mean that there was 

 no life on the world ajhthat time, but either that the 

 conditions were not favorable for the preservation of 

 fossils, or that the subsequent changes in the rocks 

 (metamorphosis) have obliterated them. There is 

 every certainty that life must have been in exist- 

 ence, but no fossil remains of animals assist us to 

 this conclusion. All of the history dwelt upon in the 

 last two chapters must have occurred during the 

 Archean age, for, with its close, all of the early 

 history had been past. 



The Silurian (2) is characterized by the presence 

 of animals in great profusion. The animals charac- 

 teristic of the age were the invertebrates ; for while 

 it is certain that vertebrates were in existence before 

 its close, they were but slightly developed in com- 

 parison with the invertebrates, and did not appear at 



