Divisions of Life and Time 



thing of the earth into the sea, directly or in- 

 directly as the case may be. This warfare 

 began when the first ridge of rock peered above 

 the level of the primeval ocean, and has been 

 carried on without a moment's intermission ever 

 since, the results of the conflict being the for- 

 mation of beds of mud or sand that later hard- 

 ened into rock. Into the mud and sand sank 

 not only the remains of animals that dwelt in 

 the lake or ocean where the beds were being 

 deposited, but those of creatures that lived 

 upon the adjacent land and perished along the 

 shore or were swept down by rivers. Hence 

 the layers of rock contain the vestiges of the 

 plants and animals that lived at the time they 

 were being formed, and these fossils serve to 

 identify the strata in which they are found. 

 So rocks above those which show no traces of 

 living things are arranged or classified accord- 

 ing to the fossils they contain, each layer or 

 stratum being termed a formation or stage. 

 Now the life of the globe has been ever vary- 

 ing with the movements of its crust, some plants 

 and animals dying out and others arising to 



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