ON THE FORMATION OF LIMESTONE BEDS. 57 



pitated : and hence a bed of limestone, co-extensive 

 with the lateral diffusion which had taken place 

 in the ocean of the bi-carbonate of lime, would be 

 formed. 



87. During the process, which we have just de- 

 scribed, by which the bi-carbonate of lime is re- 

 duced to a carbonate, a quantity of carbonic acid 

 gas is given off, precisely equal to the quantity of 

 carbonic acid gas which is precipitated with the 

 lime in the formation of a limestone bed ; that while 

 one equivalent of carbonic acid gas is precipitated 

 with the lime, the other equivalent of the gas is 

 given off, to enter into the composition of the atmo- 

 sphere.* 



88. As the carbonate of lime is insoluble in 

 water, whence was it that the encrinites of the 

 mountain limestone derived their carbonate of lime ? 

 Was it from a bi-carbonate of lime which the ocean 

 held in solution that those encrinites derived their 

 calcareous matter? Was the bi-carbonate decom- 

 posed, of which one equivalent of carbonic acid gas 

 in combination with the lime w r as appropriated by 



* An analogous process takes place in calcareous springs 

 which are charged with the bi-carbonate of lime one equiva- 

 lent of carbonic gas is given off to the atmosphere, and the 

 other equivalent in combination with the lime is precipitated. 



