AZOIC AGE. 181 



they lose themselves in the rising peculiarities of another 

 coming period or age. Thus that remarkable age, the 

 coal-bearing or Carboniferous age, which was specially 

 occupied in making and storing up coal in the strata of 

 the earth's crust, was foreshadowed by the occurrence 

 of plants similar to the coal-plants in the previous age, 

 the age of Fishes. So also mammals appeared to some 

 extent long before that age in which these animals were 

 so numerous, in many cases so monstrous, as to make it 

 proper to denominate it the age of Mammals. It may be 

 remarked, in this connection, that it is not the idea to 

 give the name of a class of animals to an age because 

 they are more abundant then than they are in any other 

 age. Thus the mollusks are really not as abundant in 

 the age to which they give their name as they are after- 

 ward in the age of Reptiles, but in the age of Mollusks 

 they are more abundant than any other class. At the 

 same time, abundant as are the mollusks in the age of 

 Reptiles, the latter then surpass them in abundance, and 

 so give the name to the age. The articulates, which do 

 not give a name to any age, have steadily increased from 

 their small beginning far back at the conclusion of the 

 Azoic age on to the age of the present. 



CHAPTER Xin. 



AZOIC AGE. 



263. Beginning of Solidification of the Earth. There 

 was a time when the earth was a liquid mass. Of 

 course, with such a degree of heat as sufficed to maintain 

 it in this condition, there was no liquid water, but the 

 heated ball was enveloped in steam. But after a time a 

 portion of the outside of the mass became solid, forming 

 a crust. Professor Hitchcock savs that it is not unlike- 



