414 EDWARD ST EI DT MANN 



indicate a higher ratio of calcium to magnesium of the present 

 lands than in the primitive lithosphere. 



2. The marginal sediments show a tendency toward more in- 

 tense anamorphism, a greater number of and more profound uncon- 

 formities than those of the interior, and a dominance of elastics in 

 those sediments which were deposited during continental expan- 

 sion. More intense anamorphism 1 of the border sediments involves 

 a selective retention of magnesium in them. 



3. Marine sediments on the present continental shelves within 

 the 100-fathom lineconsist predominantly of elastics, from 50 

 per cent to 70 per cent of the river-borne sediments being deposited 

 here. This seems to afford a fair perspective of the nature of 

 sedimentation during continental expansion. 



4. Areally the calcareous deposits constitute a minority of the 

 deep-sea deposits. The rate of accumulation of the terrigenous 

 deep-sea muds is probably vastly greater than that of the cal- 

 careous deposits. Furthermore, a considerable portion of the 

 calcareous deposits goes back into solution, and has therefore the 

 potentiality of returning to the lands. The permanent with- 

 drawal of terrigenous muds from the land areas unquestionably 

 exceeds that of calcareous deposits. This selective withdrawal 

 suggests one factor in the causation of the loss of muds from the 

 continental interiors. Since muds not only tend to absorb more 

 magnesium than calcium, but actually show a high magnesium 

 content when compared to other sediments, it is not improbable 

 that the permanent loss of muds from the continents also involves 

 a selective and permanent loss of magnesium. 



5. The selective retention of land-derived magnesium in sea 

 water may have been an important factor in causing an increase 

 in the ratio of calcium to magnesium of the lands. 



HAS THE RATIO OF CALCIUM TO MAGNESIUM IN THE RIVER 

 WATERS INCREASED WITH GEOLOGIC TIME? 



The lands have been shown to represent a higher content of 

 limestone than could have been gotten from the redistribution 

 of the principal igneous rock types which are generally accepted 



1 Ibid., 37, "Dynamic Metamorphism." 



