tJie Earth at different Epochft, ^c. 367 



Might not some cause be found which would explain, in a na- 

 tural manner, this developcmcnt and vigorous vegetation of the 

 terrestrial plants, at the most remote times of the formation of 

 the globe, and, on the other hand, the appearance only in the 

 later periods of its formation of the warm-blooded animals, or 

 those whose aerial respiration is the most active ? Might not this 

 difference in the period of the appearance of these two classes of 

 beings, depend upon the difference of their mode of respiration, 

 and upon circumstances in the state of the atmosphere, calcula- 

 ted to favour the developement of the one kind, and oppose that 

 of the other ? 



Under what form, at the period of the creation of organized 

 beings, did all the carbon exist which these beings subsequently 

 absorbed, and which occurs buried along with their remains in 

 the bowels of the earth, or which still exists diffused among all 

 the organised beings which at present cover the surface of the 

 globe ? 



It is evident that animals not extracting carbon either from 

 the atmosphere or from the soil, but only from their food, 

 vegetables alone could have procured, in an inorganic substance, 

 the carbon necessary for their growth, which carbon, through 

 their intervention, afterwards served for the nutrition of ani- 

 mals. 



We cannot conceive how, if this carbon had been in the solid 

 state, the vegetables could have assimilated it ; and besides, in 

 the formations older than those which contain the first remains 

 of vegetables, scarcely any traces of charcoal are seen. 



It must therefore have been the case, that this carbon, which 

 the plants of the primitive vegetation and of the subsequent ve- 

 getations absorbed, existed under a form calculated to afford them 

 nutrition. Now, we only know two such forms, viz. vegetable 

 mould, which, itself resulting from the decomposition of other ve- 

 getables, would lead us to reason in a circle ; and carbonic acid, 

 which, on being decomposed by the leaves of vegetables under 

 the influence of the solar light, fixes its carbon in the plant, and 

 thus contributes to its growth. 



It therefore appears to me impossible to suppose that the ve- 

 getables imbibed from any other source than the atmosphere, or 

 in any other form than that of carbonic acid, the carlx>n which 



Bb 2 



