THE SEVEN AGES OF PLANT LIFE 33 



the accumulation of plants, and the gradual sinking of 

 the land level also favoured their preservation under 

 rapidly succeeding deposits. Of the countless plants 

 growing in Europe to-day very few stand any chance 

 of being preserved as coal for the future; so that, unless 

 the physical conditions were suitable, plants might have 

 been growing in great quantity at any given period with- 

 out ever forming coal. But now that the geology of the 

 whole world is becoming better known, it is found that 

 coal is by no means specially confined to the Coal Measure 

 age. Even in Europe coals of a much later date are worked, 

 while abroad, especially in Asia and Australia, the later 

 coals are very important. For example, in Japan, seams 

 of coal 14, 20, and even more feet in thickness are worked 

 which belong to the Tertiary period (see p. 34), while in 

 Manchuria coal 100 feet thick is reported of the same age. 

 When these facts are considered it is soon found that all 

 the statements made about the unique vegetative luxuri- 

 ance of the Coal Measure period are founded either on 

 insufficient evidence or on no evidence at all. 



The plants forming the later coals must have had in 

 their own structure much that differed from those form- 

 ing the old coals of Britain, and the gradual change in 

 the character of the vegetation in the course of the suc- 

 ceeding ages is a point of first-rate importance and 

 interest which will be considered shortly in the next 

 chapter. 



CHAPTER IV 

 THE SEVEN AGES OF PLANT LIFE 



Life has played its important part on the earth for 

 countless series of years, of the length of whose periods 

 no one has any exact knowledge. Many guesses have 

 been made, and many scientific theories have been used 

 to estimate their duration, but they remain inscrutable. 

 When numbers are immense they cease to hold any 



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