THE STORY OF THE EARTH 223 



public is not aware of them, and the effects they pro- 

 duce in a single lifetime are not observable. Yet the 

 results of age-long slow movement are stupendous. 



In my Romance of the Rocks I represented the story 

 of the earth as being, so to say, inscribed in several 

 books, each book containing chapters, and each chapter 

 being composed of sections. The books are made of 

 stone. Each book tells the story of an Era embracing 

 vast time, and each chapter deals with a Period of the 

 Era. Again, each section of a chapter has reference 

 to a subdivision of a Period. But to make the simile 

 correct one must conceive of all the books as being 

 integral parts of one great volume, the theme of which 

 is continuous throughout. We know of no sudden 

 endings or capricious restarts in Nature, no changes of 

 policy, no alteration of law. Development has always 

 been continuous. While for the sake of convenience 

 of description, and for the due relation of older and 

 newer, the geologist speaks of Eras and Periods, he does 

 not imply that one Era is absolutely cut off from another, 

 for he knows that Eras and Periods are not separated 

 by clear-cut lines of demarcation. On the reverse, he 

 realizes that the Periods of an Era shade off one into 

 another, as is also the case with Eras themselves. 



Let it be understood that the stratified rocks have 

 been deposited through incalculable time. The oldest 

 of them are so old that it were foolish to even guess 

 their age in years. But we know something of the 

 order in which they were deposited, and their fossil 

 contents enable us to decide which rocks are very old, 

 which are less old, and which are of comparatively 

 recent date. Within the range of the Secondary rocks 



