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COMMENCEMENT OF OPtGANIC LIFE. 



SEA PLANTS, CORALS, ETC. 



"VVe can scarcely be said to have passed out of these 

 rocks, when we begin to find new conditions in the earth. 

 It is here to be observed that the subsequent rocks are 

 formed, in a great measure, of matters derived from the 

 substance of those which went before, but contain also 

 beds of limestone, which is to no small extent composed 

 of an ingredient w^hich has not hitherto appeared. Lime- 

 stone is a carbonate of lime, a secondary compound, of 

 w^hich one of the ingredients, carbonic acid gas, presents 

 tlie element carbon, a perfect novelty in our progress. 

 Whence this substance? The question is the more 

 interesting, from our knowing that carbon is the main 

 ingredient in organic things. There is reason to believe 

 that its primeval condition was mainly that of a gas 

 diffused in the atmosphere, although portions of it are 

 also found occasionally issuing from the interior of the 

 earth. The atmosphere still contains about a two- 

 thousandth part of carbonic acid gas, forming the grand 

 store from which the substance of each year's crop of 

 herbage and grain is derived, passing from herbage and 

 grain into animal substance, and from animals again 

 rendered back to the atmosphere in their expired breath, 

 so that its amount is never impaired. Knowing this, 



