EVOLUTION OF LIMESTONE AND DOLOMITE 345 



metamorphism and sedimentation or by a progressive change 

 in the calcium and magnesium content of the lands. It cannot 

 very well be assumed that the nature of the agents and processes 

 which contribute calcium and magnesium to the sea has undergone 

 any marked change during geologic time. The continuity of the 

 life record, the uniformity of sedimentation, and the duplication 

 of climatic conditions down to the remote past speak against it. 

 How then could the constitution of the lands, apparently the only 

 remaining alternative, undergo a progressive change which in 

 turn caused a progressive increase in the ratio of calcium and 

 magnesium contributed to the sea, under uniformitarian processes ? 

 The answer to this problem is sought in the nature of the redis- 

 tribution of calcium and magnesium in consequence of meta- 

 morphic and depositional processes. 



[To be continued] 



