226 CLARKE— SOME GEOCHEMICAL STATISTICS. [April 20, 



Per Cent. Metric Tons X10I2. 



CI 55292 26,406 



Br 188 89.8 



SO4 7692 3,673s 



CO3 207 98.8 



Na 30.593 14,611 



K 1. 106 528.2 



Ca 1. 197 571-7 



Mg _3-725 1,779 



100.00 47,758 



The average specific gravity of 958 igneous rocks, collected in 

 Washington's Tables, is 2.737; and one cubic kilometer of rock 

 should therefore weigh 2,737,ocx),ooo metric tons. From the aver- 

 age of the Survey analyses given on p. 221 ante, the mean percentage 

 of sodium in igneous rocks is 2.51, and from Washington's average 

 2.90. Hence the sodium contained in the ocean, 14,611 X 10^- metric 

 tons, would be furnished by the complete decomposition of the fol- 

 lowing volumes of igneous rock : 



From the Survey average, 212,680,000 cubic kilometers. 



From Washington's average, 184,080,000 cubic kilometers. 



Some sodium, however, remains in the sedimentary rocks, 

 namely, 0.90 per cent, as computed from the reduced average anal- 

 ysis. On comparing this figure with those for the total sodium of 

 the igneous rocks, the volumes of the latter actually decomposed 

 become, approximately, 



Survey, 318,950,000 cubic kilometers. 



Washington, 260,160,000 cubic kilometers. 



In order to determine the volume of the sedimentaries these 

 figures require two small corrections. First, a deduction must be 

 made for the soda, potash, lime and magnesia lost during erosion, 

 and now represented by the corresponding radicles in the ocean. 

 Secondly, for the difiference in density between the original rocks 

 and the sedimentaries, indicated by the ratios 2.737:2.6. The first 

 correction is approximately 24,095 X 10^- metric tons, or 8,803,000 

 cubic kilometers. Making the corrections, we have, for the actual 

 volume of the sedimentaries, 



Survey, 326,590,000 cubic kilometers, or 78,338,000 cubic miles. 



Washington, 264,600,000 cubic kilometers, or 63,481,000 cubic 

 miles. 



