PREFACE. 



I have endeavoured to tell the story of the 

 Earth so that its past history helps to explain its 

 present condition. 



Explanations are given of the nature of the 

 common materials which form rocks, of the ways 

 in which they rot upon each other, and of the 

 means by which they may be distinguished. 



The story of the Earth is divided into epochs 

 by layers of rock which rest on each other and 

 to the surface of the visible land, and to the 

 floor of the ocean. 



Geological time cannot be defined in years. 

 The time occupied by an existing river like the 

 Rhine or the N l river, in excavating the 



gorge through which it flows, dates back beyond 

 the antiquity imagined for man by historians. 

 Yet this incident in sculpture of the Earth's sur- 

 face is subsequent to the newest of the regular' 

 layers of rock. It is convenient to forget the 

 human standard of time, and think of a period of 

 geological time as the age when some rock, such 

 as coal, accumulated, or when an extinct plant or 

 animal was dominant on the Earth. 



Fossils are the remains of plants and animals 

 by which each period of by-gone time is distin- 

 guished. 



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