424 EDWARD STEIDTMANN 



and inorganic agencies. The percentage of calcium carbonate 

 which is deposited from the sea is higher than that of magnesium 

 carbonate, and from field and laboratory evidence it is inferred 

 that the proportions of the two carbonates deposited are in some 

 direct relation to their proportions in the rivers which bring them 

 to the sea. Hence, there is a selective return of calcium to the 

 lands. 



It is therefore inferred that the evolution of the limestones 

 and dolomites has been in response to the gradual increment of 

 calcium over magnesium in the solutions contributed to the sea, 

 a tendency arising primarily from physical-chemical causes, aided 

 or accelerated by organic processes working harmoniously with the 

 inorganic environment. 



For illustration, it may be assumed that sedimentation began 

 during continental expansion when the lands had the composition 

 of an average igneous rock. From the known results of meta- 

 morphic processes, it would follow that the solutions contributed 

 to the sea had a higher calcium to magnesium ratio than the lands 

 from which they were derived, and that the residuals had a higher 

 proportion of magnesium to calcium than the original rocks. A 

 part of the residuals, particularly the muds, are subject to selective 

 transportation to the continental margin and the deep sea. Accept- 

 ing the hypothesis of the permanence of oceans and the continents, 

 those deposited in the deep sea are permanently removed from 

 the continents. The calcium and magnesium salts interact with 

 the materials of the ocean bottom and enter into the constitution 

 of silicates, carbonates, and other compounds, or they may inter- 

 act with other constituents in the water, and be precipitated prin- 

 cipally as the carbonates. Magnesium would tend to interact 

 more actively with the muds of the bottom than calcium. Calcium 

 would tend to be more insoluble in shallow water than in the 

 deeps, while the opposite tendency probably characterizes mag- 

 nesium. Magnesium salts in general are more soluble in sea 

 water than calcium salts. Organic precipitation, apparently only 

 an adaptation to conditions of chemical equilibrium already 

 existing, would be particularly effective in abstracting calcium 

 from warm, shallow seas. The relative solubility of the materials 



