140 



THE BEGINNINGS OF LIFE, 



' Vegetables 







continued incessantly to abstract a 

 portion of the carbon of the air. and thus rendered 



and their transformation into soil; for this kind of decomposition is 

 owing essentially to the abstraction of a portion of the carbon of the 

 wood by the oxygen of the air : and if the atmosphere contained less 

 oxygen and more carbonic acid, the decomposition in question must 

 have been without doubt both more difficult and slower. Hence the 

 accumulation of vegetable debris in extensive beds, even in circumstances 

 and from vegetables which, in the actual state of the atmosphere, would 

 give rise to no such layers of combustible material.' 



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It e^^^y c ve. 



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of a 



tree?? 



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K of ^l^''' 



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''1 the surfac 



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<= On the other hand, this difference in the com^ 

 position of the atmosphere, so favourable to the de- 

 velopment, growth, and preservation of vegetable 

 matter, must have proved a bar to the existence of 

 animals, particularly of warm-blooded animals, whose 

 respiration, as it is more active, also requires a purer 



■ 



air : during this first period, consequently, not a single 

 animal breathing air appears to have existed. 



^ During this period the atmosphere must have been 

 purged of some portion of the excess of carbonic acid 

 which it contained, by the vegetables which then existed - 

 these assimilated it first, and subsequently buried it in 



* 



the state of coal in the bowels of the earth. It is after 



this first period, in the course of our second and third to the developme; 



periods, that this immense variety of monstrous reptiles simoltaneous exist 



makes its appearance, animals which, by the nature of 



their respiration, are capable of living in an atmosphere 



of much less purity than that which warm-blooded 



r 



animals require, and were the heralds and precursors 

 of these. 



till exist in 

 its surface. 



(Would it not t 



atmosphe 



re 



had n 



It 



hich could alone 

 -blooded 



warm 



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the inverse i; 



mke to maint 

 which is 

 present period 

 ) then, is tl 



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"iterchanges 



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lobe. Th 



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inorga 



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