EVOLUTION OF LIMESTONE AND DOLOMITE 411 



area of the lands. Could not a depletion of the calcium carbonate 

 content of the sea result from intensified deposition on the sub- 

 merged continents ? What then ? The solubility of the calcium 

 carbonate toward the shallows from the deeps, a process now in 

 operation as shown by the results of the Challenger expedition, 

 would be accelerated. The selective accumulation of limestones 

 on the continents as shown by geologic sections would be con- 

 summated. 



Significance of the deposition of muds in the ocean basins. — The 

 composition of river muds is variable, depending upon the com- 

 position of the lands over which the rivers flow. The longer the 

 delta region of a river, in general, the smaller probably will be 

 the amount of soluble materials in the muds. The Nile and 

 Mississippi muds may be regarded as typical of the larger streams 

 of the world. In an analysis of Mississippi mud 1 the ratio of 

 lime to magnesia is 1 . 1 1 : 1 (Table XIX) . The ratio of lime to 

 magnesia in an analysis of Nile 2 mud is 1.82:1. 



TABLE XIX 



Table Showing Lime and Magnesia Ratios of Nile and Mississippi Muds 



The analyses of Nile and Mississippi muds show a relatively 

 high content of magnesia, as compared with other sediments. It 

 follows that if any large proportion of muds is lost from the lands 

 through deposition in the ocean basins, it would mean a selective 

 abstraction of magnesia from the lands, considering the quanti- 

 tative importance of the muds. The ratio of suspended material 

 to total dissolved solids in the Mississippi at Memphis, according 

 to Dole's yearly average, is 2.3:1. Mellard Reed has estimated 

 that the proportion of suspended to dissolved materials in the 

 river waters of the world is 66:33, or 2:i - Approximately one- 

 half of the dissolved material is calcium carbonate. The ratio 



1 By C. H. Stone, Science, XXIII (1906), 634. 



2 Analysis D., Bull. 330, U.S.G.S., 429. 



