56 ON THE FORMATION OF LIMESTONE BEDS. 



the equivalents of the bi-carbonate will be given off, 

 and the other equivalent will remain in combination 

 with the lime, which is the carbonate of lime a 

 salt that is insoluble in water and is, therefore, 

 precipitated. If, therefore, the ocean, at a remote 

 period, held lime largely in solution, as some geo- 

 logists suppose, and carbonic acid gas escaped then, 

 as it does now, from clefts or fissures in the crust of 

 the earth, it is evident, that if, at a great depth, 

 this gas escaped from a fissure at the bottom of the 

 ocean, it would combine with the lime in solution, 

 and, under the great pressure of the superincumbent 

 waters, would form the bi-carbonate of lime a salt 

 that is soluble in water. Now, as every soluble 

 body has a tendency to diffuse itself through the 

 menstruum in which it is dissolved, the bi-carbonate 

 of lime, thus formed, would diffuse itself in the 

 waters laterally and vertically, the vertical diffusion 

 being co-extensive with the lateral diffusion; but 

 during the diffusion of the bi-carbonate of lime to- 

 wards the surface of the ocean, the superincumbent 

 pressure of the waters would be gradually removed, 

 until, at length, the bi-carbonate would part with 

 one of its equivalents of carbonic acid gas, and 

 would thus be reduced to a carbonate of lime, 

 which, not being soluble in water, would be preci- 



