XO. 5 STUDY OF CHEMICAL DENUDATION — CLARKE 17 



relative proportions of the CO3 radicle become 3.78 : 13.78, or 1 : 3.4 

 nearly. The last figure should be higher, because of the more rapid solu- 

 tion of the limestones, but if we accept the ratio as it stands we may use 

 it to determine the approximate proportions of the CO3 radicle derived 

 from limestones and from the atmosphere acting upon crystalline rocks. 

 On this basis, 8 per cent, of CO3 should be deducted from the percentage 

 in the river waters, together with the 0.9 per cent, of NO3. Making the 

 subtraction from the total river load of dissolved matter, 2,735,000,000 

 tons, there remains 3,491,585,000 tons, or about 63.3 tons per square mile 

 on the average, for the 40,000,000 of square miles of land which are 

 assumed to drain into the ocean. This implies a lowering of the land by 

 solvent denudation at the rate of one foot in 29,941 years, or 30,000 in 

 round numbers. The last estimate may be subject to large future correc- 

 tions, but probably it is correct to within 10 per cent. 



It is possible, mth the data now in hand, to take still another step and 

 determine approximately the quantity of chemical sediments annually 

 precipitated in the ocean. For this purpose we may first, knowing the 

 average composition of river waters, and also their total load of dissolved 

 inorganic matter, compute the actual amount of eacli radicle poured into 

 the ocean in one year. The total amount so added is 3,735,000,000 metric 

 tons, distributed as follows : 



CO3 961,350,000 tons 



SOi 332,030,000 " 



CI 155,350,000 " 



NO3 24,614,000 " 



Ca 557,670,000 " 



Mg 93,264,000 " 



Na 175,040,000 " 



K 41,299,000 " 



R„03 75,213,000 " 



Si02 319,170,000 " 



2,735,000,000 " 



If, from each of these quantities we subtract the amount annually re- 

 tained in solution by the sea, the difference will represent the amount 

 precipitated. To do this, an assumption must be made as to the age of 

 the ocean ; but whatever probable figure is thus assumed, the results will 

 be of the same order of magnitude. For example, the ocean contains 

 553.8 X 10^' metric tons of dissolved calcium, which quantity, divided by 

 the assumed age, gives the annual increment. If the age of the ocean 

 is 100,000,000 years, the annual addition of calcium is 5,538,000 tons ; if 

 only 50,000,000 years it is 11,056,000 tons. Subtracting these quantities 

 from the total calcium of the river waters the remainders become 552,- 

 143,000 and 546,614,000 tons respectively, the difference being much less 



