METHYLOTIC ORIGIN OF DOLOMITES. 95 



portion, carrying it off as a bicarbonate in solution without re- 

 moving the magnesian constituent. According to Dr. Apjohn, 

 " it is not improbable that this removal of the carbonate of lime 

 may proceed until what remains behind contains the two car- 

 bonates in the ratio of atom to atom/'' or in the proportion they 

 are presumed to be in dolomite. This decalcifying process, it 

 is conceivable, ought in many cases to be consummated by the 

 removal of all the calcareous matter, and the consequent con- 

 version of what was once a dolomitic limestone into a residual 

 mass of magnesite. But it is extremely doubtful that any thing 

 of the kind on a commensurate scale is known. 



