32 



SEA PLANTS, CORALS, ETC. 



conditions, one in which organic life has probably played 

 a part. 



It is not easy to suppose that, at i.nis period, carbon waa 

 adopted directly in its gaseous form into rocks ; for, if so, 

 why should it not have been taken into earlier ones also ? 

 But we know that plants take it in, and transform it into 

 substance ; and we also know that there are classes of 

 animals (marine polypes) which are capable of appropri- 

 ating it, in connection with lime (carbonate of lime) 

 from the waters of the ocean, provided it be there in solu- 

 tion ; and this substance do these animals deposit in mass- 

 es (coral reefs) equal in extent to many strata. It has even 

 been suggested, on strong grounds of probability, that a 

 class of limestone beds are simply these reefs subjected 

 to subsequent heat and pressure. 



The appearance, then, of limestone beds in the early part 

 of the stratified series, may be presumed to be connected 

 with the fact of the commencement of organic life upon 

 our planet, and, indeed, a consequent and a symptom of it. 



It may not be out of place here to remark, that carbon 

 is presumed to exist largely in the interior of the earth, 

 from the fact of such considerable quantities of it issuing 

 at this day, in the form of carbonic acid gas, from fissures 

 and springs. The primeval and subsequent history of this 

 element is worthy of much attention, and we shall have 

 to revert to it as a matter greatly concerning our subject 

 Delabeche estimates the quantity of carbonic acid gas 

 locked up in every cubic yard of limestone, at 16,000 

 cubic feet. The quantity locked up in coal, in which it 

 forms from 64 to 75 per cent., must also be enormous. 

 If all this were disengaged in a gaseus form, the constitu- 

 tion of the atmosphere would undergo a change, of which 

 the first effect would be the extinction of life in all land 

 animals. But a large proportion of it must have at 

 one time been in the atmosphere. The atmosphere would 

 then, of course, be incapable of supporting life in land 

 animals. It is important, however, to observe that such 

 an atmosphere would not be inconsistent with a luxuriant, 

 land vegetation ; for experiment has proved that plants 

 will flourish in air containing one-twelfth of this gas, or 

 166 times more than the present charge of our atmosphere. 

 The results which we observe are perfectly consistent 

 with, and may be said to presuppose an atmosphere highly 

 charged with this gas, from about the close of the prima- 



