8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 56 



The total area accounted for is 28,000^000 square miles, with a mean 

 solvent denudation of 68.4 tons. The. incompleteness of the figures is 

 due to the fact that large areas of the earth's land surface either do not 

 drain into the ocean, or, as in the cases of Arabia, the coast of Peru, etc., 

 contribute little or nothing to it. There is, of course, local denudation in 

 areas like the Great Basin of the United States and the Caspian depres- 

 sion; but that does not fall within the scope of the present discussion. 

 Furthermore, the circumpolar regions such as Greenland and the Antarctic 

 continent have no large rivers, and must be left out of account. The total 

 land area to be considered, that is, the area which contributes to the 

 salinity of the ocean, is, according to Murray, 39,697,400 square miles, or 

 40,000,000 in round numbers. Assuming that the figures so far given for 

 28,000,000 square miles represent a fair average, the total amount of 

 saline matter carried into the ocean by the river drainage of the world is 

 2,735,000,000 metric tons, an estimate only a little more than half that 

 given by Murray. 



The composition of the saline matter thus carried into the ocean is 

 given in the next table. The averages for Asia and Africa are made up in 

 the manner already indicated: the final general mean roughly weights 

 the individual means proportionally to the number of tons given in the 

 last column of the foregoing table : 



N. America. 8. America. Europe. Asia. Africa. General mean. 



COs 33.40 32.48 39.98 36.61 32.75 35.15 



SO4 15.31 8.04 11.97 13.03 8.G7 12.14 



CI 7.44 5.75 3.44 5.30 5.66 5.68 



NOs 1.15 .62 .90 .98 .58 .90 



Ca 19.36 18.92 23.19 21.23 19.00 20.39 



Mg 4.87 2.59 2.35 3.42 2.68 3.41 



Na \ 9.23 5.03 4.32 6.42 4.90 6.40 



K J 1.95 2.75 1.54 2.35 1.51 



R2O3 64 5.74 2.40 1.96 5.52 2.75 



Si02 8.60 18.88 8.70 9.51 17.89 11.67 



100.00 100.00 100.00 100.00 100.00 100.00 



Weight .... 10. 4. 6. 11. 7. 



The final mean, regardless of possible corrections, is curiously near the 

 average figures for three great rivers, the Mississippi, Amazon, and Nile. 

 It is probably rather high in silica, but on the whole it is as near to the 

 truth as can be determined from the existing data. The greater rivers 

 of Africa and Asia are yet to be studied, and much more should be done 

 in South America. In the analyses reported by Dole, sodium and potas- 

 sium are rarely discriminated, and hence the two radicles are given to- 

 gether as sodium alone. This error, however, is compensated by the 

 excessive and evidently erroneous determinations of potassium in the Nile 



