368 M. Brongniart (yn the Vegetation of 



is still found in all the vegetables and animals existing, and that 

 after serving for their nutrition, has been deposited in the 

 form of coal, lignite, or bitumen, in the different sedimentary de- 

 posites. If we then suppose that all this carbon, in the state of 

 carbonic acid, was diffused in the atmosphere previous to the 

 creation of the first organised beings, it will be seen that the at- 

 mosphere, instead of containing less than a thousandth part of 

 carbonic acid, as is now the case, must have contained a quanti- 

 ty of it which cannot be exactly estimated, but which was, per- 

 haps, 8, 4, 5, 6 or even 8 per cent. 



The researches of M. Theodore de Saussure have shewn that 

 this proportion of carbonic acid, so far from proving hurtful to 

 vegetation, is very favourable to it, when the plants are exposed 

 to the sun. This very probable difference in the nature of the 

 atmosphere, may, therefore, be considered as one of the most 

 powerful causes which have exerted their influence upon the very 

 active and very remarkable vegetation of our first period. 



But this very circumstance must, on the contrary, have been 

 detrimental to the decomposition of the remains of dead vegeta- 

 bles, and have retarded their transformation into mould ; for this 

 mode of decomposition is essentially dependent upon the abstrac- 

 tion of a part of the carbon of the wood by the oxygen of the 

 air ; and if the atmosphere contained less oxygen and more car- 

 bonic acid, this decomposition must, without any doubt, have 

 been more difficult and more slow. Hence the accumulation of 

 those remains of vegetables in kinds of peat deposites, even under 

 circumstances and with vegetables, which, in the present state of 

 the atmosphere, would not give rise to the formation of similar 

 beds of combustible. 



On the other hand, this difference in the composition of the 

 atmosphere, so favourable to the growth and preservation of ve- 

 getables, would have been an obstacle to the existence of ani- 

 mals, and especially to that of warm-blooded animals, whose 

 more active respiration requires a purer air. Accordingly, du- 

 ring this first period, there does not appear to have existed a 

 single animal that respired air. 



During this period, the atmosphere was freed of a part of 

 its excess of carbon, by the vegetables which grew upon the land, 

 which assimilated it, and were afterwards buried in the state of 



