AND THEIR DESCENDANTS 



We shall not press on the reader in a volume of this 

 kind any detailed classification of the strata, but he will 

 like to know the names of the five great periods into which 

 geologic time is divided. 



The first period was the Archaean, embracing the periods 

 of the earliest rocks wherein few or no traces of life occur. 



The second period was the Palaeozoic (ancient life) or 

 Primary, which includes the long succession of ages during 

 which the earliest types of life existed. 



The third period was the Mesozoic (middle life), com- 

 prising a series of ages when more advanced types of life 

 flourished. 



The fourth period was the Cainozoic (recent life) or 

 Tertiary period, when such types of life as we know and see 

 now appeared. This period, however, does not include man. 



The fifth period is the Quaternary or Post-Tertiary and 

 Recent, and includes the time since man appeared on the 

 earth. 



These divisions were not of the same length. The 

 Palaeozoic ages were probably far, far longer than those of 

 any other division, while the Quaternary period is shorter 

 than any of those which preceded it. Each of these main 

 divisions is divided further into systems or shorter periods 

 (just as the dynasties of ancient Egypt could be sub- 

 divided into reigns). Though the broad outlines of the 

 sequence of the living things which existed in those 

 periods has been the same all over the world, many local 

 differences may be traced in the nature and grouping of 

 the sedimentary materials in which the remains of the 

 living things of these epochs have been preserved. 



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