xxiv INTRODUCTION. 



eludes the constituents of the sea and atmosphere as well; 

 these two constitute about 7 per cent of the whole, 93 per cent 

 being solid rocks. 



RELATIVE ABUNDANCE OF THE ELEMENTS TO A DEPTH OF TEN KILOMETERS. 



SOLID CRUST OCEAN MEAN, 



(93 PER CENT). (7 PER CENT). INCLUDING AIR. 



49.98 



2 5-30 

 7.26 

 5.08 



3-5' 

 2.50 



2.28 

 2.23 

 0.94 

 0.30 



0.21 

 0.15 

 O.O9 

 O.O7 

 O.O4 

 0.03 

 O.O2 

 O.O2 

 O.OI 



It will be noted that one-half of the total consists of oxygen, 

 and that nearly 86% (or 47.29% of the 49.987^) of this 

 amount is contained in the solid rocks; nearly 2.50% of the 

 remainder in sea and other water; and .41% in the atmosphere, 

 in the free condition, in which it serves for the respiration of 

 animals and plants, and for the various processes of slow and 

 rapid combustion, or " oxidation." This relatively small pro- 

 portion of the whole, is, nevertheless, the most directly im- 

 portant for the maintenance of organic life. 



Oxids Constitute Earth's Crust. The vast predominance 

 of oxygen in the above list suggests at once that most of the 

 other elements must exist in combination with it, i. c., as 

 " oxids." H. S. Washington l has lately revised the esti- 

 mates heretofore made, on the basis of a very large number of 

 analyses made by him and others, of rocks within the United 

 States, and gives the following table; alongside of which is 

 placed a revised estimate by Clarke, which also includes rocks 

 from abroad; both being given in terms of oxids of the several 

 elements. 



1 U. S. Geol. Survey, Professional Paper No. 14, p. 108. 



