THE BEGINNINGS OF LIFE. 139 



that vegetables can have derived from any other source 

 than the atmosphere, and in the state of carbonic acid, 

 the carbon which is found in all existing species of 

 plants and animals,, as well as that which, after having 

 served the vast primeval forests for sustenance, has 

 been deposited, under the form of coal, lignite, and 

 bitumen, in the different sedimentary strata of the 

 earth. If we suppose, then, that the whole of this 

 carbon was diffused through the atmosphere in the 

 shape of carbonic acid prior to the creation of organ- 

 ized beings, we shall see that the atmosphere, instead 

 of containing less than the one-thousandth part of its 

 bulk of carbonic acid as at present, must have con- 

 tained a quantity which it is not easy to estimate 

 exactly, but which was perhaps in the proportion of 

 3, 4, 5, 6, and even 8 per cent/ 



But the experiments of M. Saussure have shown that 

 such a super-abundance of carbonic acid in the at- 

 mosphere, far from being detrimental, is positively 

 favourable to the life of plants when they are at the 

 same time exposed to the influence of the solar light 

 and heat. So that, as M. Brongniart says, c This 

 highly probable difference in the constitution of the 

 atmosphere may, therefore, be regarded as one of the 

 causes influencing most powerfully the more active and 

 very remarkable vegetation of the first organic period 

 of our globe l . 



1 ' But this same circumstance must, on the contrary, have interfered 

 materially with the decomposition of the remains of dead vegetables 



