Studies in the Calcitc Group. 233 



shown in these cases is due to errors of analysis. There are, 

 however, eleven analyses or about one tenth of the total number 

 studied that show over i per cent of extra MgCO^. Therefore, 

 it seems most likely that mag'nesium carbonate may occitr in this 

 way in dolomite. The conditions necessary for its occurrence 

 are certainly much less common than in the similar case of 

 CaCO.,. 



