412 EDWARD STEIDTMANN 



of suspended materials or muds to calcium carbonate is about 

 4.4:1, which argues for a great deficiency in muds in the sedi- 

 ments now forming as compared with the proportion got by distribut- 

 ing average igneous rock under conditions most favorable to the 

 deposition of elastics, namely, the condition of continental expan- 

 sion. This is in line with the fact that the present lands represent 

 an accumulation of limestones. Of the muds now carried to the 

 sea, the major portion are deposited on the continental shelves, and 

 therefore have the potentiality of again becoming a part of the 

 land surface. J. W. Barrell 1 estimates that from 50 to 70 per 

 cent of the solids brought down to the sea by rivers is deposited 

 within the 100-fathom line. But many of the large world streams, 

 the Amazon, the Congo, Indus, Ganges, and others, have their 

 terminations near the 100-fathom line. Amazon muds have been 

 traced to a distance of 300 miles from the mouth. Barrell esti- 

 mates that from 20 to 50 per cent of the muds from the rivers are 

 deposited beyond the 100-fathom line, and are thus permanently 

 withdrawn from the lands. This estimate is entirely in harmony 

 with the deficiency of elastics in geologic sections, and with the 

 probable withdrawal of magnesium from the lands which is regis- 

 tered in the decreasing magnesium content of limestones in going 

 up the geologic time scale. But the loss of muds from the lands 

 may have been even greater in the past, since many large streams 

 in various latitudes have submerged channels which in some cases 

 extend to the edge of the 100-fathom line. On the other hand, 

 the percentage loss of muds undoubtedly was relatively much less 

 during periods of widespread continental submergence. But 

 during such periods, the total mud transported was very much 

 less, owing to the smaller relief of the lands and their floral blanket 

 resulting from the moderate, equitable climatic conditions which 

 appear to have accompanied the expansion of the seas. During 

 such periods, muds were accumulating on the lands, until periods 

 of continental uplift, like the present, accelerate their transpor- 

 tation toward the continental margins and the deep sea. 



Does the ratio of calcium to magnesium in the sea show a selective 

 loss of magnesium from the lands with geologic time? — The ratio 

 of calcium to magnesium in the river waters of the world, taking 

 1 J. W. Barrell, Jour. Geol., XIV, 346. 



