COMPOSITION OF THE LITHOSPHERE. 



933 



sea is 1,935,000,000 cubic miles (8,075,000,000 cubic kilometers). Of this 

 amount 302,000,000 cubic miles (1,260,000,000 cubic kilometers) are ocean 

 and 1,633,000,000 (6,815,000,000 cubic kilometers) are solid matter. The 

 mass of the atmosphere is equivalent to that of 1,268,000 cubic miles 

 (5,292,000 cubic kilometers) of water, the unit of density. "To sea water 

 we may assign a density of 1.03, which is a trifle too high, and to the solid 

 rocks a specific gravity not lower in average than 2.5, nor much higher 

 than 2.7. With these values we can get the following expression for the 

 percentage composition of the known matter of the globe : 



Relative masses of air, sea, and earth's crust. 



In short, we may regard the earth's crust, to a depth of 10 miles [16.1 

 kilometers], as composed essentially of 93 per cent solid and 7 per cent 

 liquid matter, treating' the atmosphere as a small correction.'" 1 



A large number of elements have been discovered on the earth, but of 

 these, according to Clarke, only 21 each constitute as much as 0.01 per cent 

 of the outer part of the lithosphere, and need be considered in this chajjter. 

 Those elements which compose more than 1 per cent may be regarded as 

 abundant and those which form less than 1 per cent as subordinate. Of 

 the former class there are only eight, viz: Oxygen, silicon, aluminum, iron, 

 calcium, magnesium, sodium, and potassium. Between the least plentiful 

 of the abundant class and the most plentiful of the subordinate class there 

 is a very considerable break, for potassium, the least plentiful of the 

 abundant elements, makes up about 2.3 per cent of the lithosphere, while 

 titanium, the most abundant of the subordinate elements, composes only 

 about 0.4 per cent of the lithosphere. 



In the chemical laboratory of the United States Geological Survey a 

 very large number of analyses of rocks have been made. Clarke has 



"Clarke, F. W., The relative abundance of the chemical elements: Bull. U. S. Geol. Survey, No. 

 78, 1891, pp. 34-35. 



